Rambam- Yesodei HaTorah- Chapter 9 Halacha 4: Prophets Do Not Decide The Law, For 'It Is Not In Heaven!"

וכן אם עקר דבר מדברים שלמדנו מפי השמועה או שאמר בדין מדיני תורה שה' צוה לו שהדין כך הוא והלכה כדברי פלוני הרי זה נביא השקר ויחנק. אע"פ שעשה אות. שהרי בא להכחיש התורה שאמרה לא בשמים היא. אבל לפי שעה שומעין לו בכל:

So too, if the prophet contradicts something that we learned from an oral tradition or says one of the laws of the Torah is [a specific way] because G-D commanded him that the law is so and the law follows so-and-so's opinion, this is a false prophet and he should [be put to death] through strangulation. [This is true] even if he performs signs since he came to destroy the Torah, since it says(Devarim 30:12) "It is not in heaven." However, we listen to him with all [commandments that are to last] for a finite amount of time.

Why is it so bad for a prophet to tell us which Rabbi to side with? He is not telling us a new law, only telling us which one of the Rabbis is favored by G-D. Why should this lead to him being put to death? One answer is given by the Maamer Mordechai:

לא בשמים היא וכו'. נ"ב אין להקשות ממ"ש בריש הפרק ויאמר שה' שלחו להוסיף מצוה וכו' דמשמע דוקא כשבא להוסיף או לגרוע הוא דנקרא נביא השקר אבל באומר הלכה כפלוני (דאיהו) [דאינו] מוסיף ולא גורע לא דהא גם הכא הוי שינוי דהא כיון דכתיב לא בשמים היא א"כ גם אינה בשמים להכריע הדין עם מי וא"כ כשזה בא ואמר הלכה כפלוני ואומר שה' שלחו א"כ נמצא דמכחיש כתוב דכתיב לא בשמים היא והכי דייקי דברי רבינו ז"ל ועיין בכ"מ ובפר"ח ודוק.

It is not in heaven, etc: This requires explanation. One should not ask based on what it says in the beginning of the chapter "The [false prophet] will say that G-D sent him to add a law, etc." That this seems to imply specifically when the [false prophet] tries to add or take away [a law] that he is called a false prophet, but if he says the law follows so-and-so, that [the false prophet] is not adding or taking away [a law, he is] not [put to death.]   This [is faulty reasoning] because [a prophet telling us which Rabbi to follow] is a change [from normative Jewish practice] because it is written (Devarim 30:12) "It is not in Heaven." Therefore, it is not in heaven to decide who the law follows. If so, when this [prophet] comes and tells us, "The law is like so-and-so," and he says, "G-D sent me," we find that he is extinguishing the verse that writes (ibid), "It is not in heaven." This is the reasoning of the [Rambam]. 

The Torah tells us that no one is allowed to add laws or subtract laws from the list of commandments. However, the verse (Devarim 4:2) "You shall not add to the word which I am commanding you, nor take away from it, that you may keep the commandments of the Lord your God which I command you," only tells us that the prophet is not allowed to come and make up a new commandment. From where do we know that their status as a prophet has no authority over us in any matters of permanent law? That comes from the verse (Devarim 30:12) of "It is not in heaven." This verse teaches us that once the Torah was given, the Rabbis now have authority over the law and not G-D. Human logic and reasoning is how we decide matters and not through divine intervention. This is a foundational principle of Judaism and must be understood. The majority rules what is law, not G-D. As demonstrated in Babba Matzia 59b by the oven of Aknai as was described in the previous mishna.    

Rambam- Yesodei HaTorah- Chapter 9 Halacha 3: To What Extent Must We Listen To The New Prophet

וכן נביא שעבר על דברי עצמו והכובש נבואתו חייב מיתה בידי שמים ובשלשתן נאמר אנכי אדרוש מעמו. וכן אם יאמר לנו הנביא שנודע לנו שהוא נביא לעבור על אחת מכל מצות האמורות בתורה או על מצות הרבה בין קלות בין חמורות לפי שעה מצוה לשמוע לו. וכן למדנו מחכמים ראשונים מפי השמועה בכל אם יאמר לך הנביא עבור על דברי תורה כאליהו בהר הכרמל שמע לו חוץ מעבודת כוכבים. והוא שיהיה הדבר לפי שעה. כגון אליהו בהר הכרמל שהקריב עולה בחוץ וירושלים נבחרת לכך והמקריב בחוץ חייב כרת. ומפני שהוא נביא מצוה לשמוע לו וגם בזה נאמר אליו תשמעון. ואילו שאלו את אליהו ואמרו לו היאך נעקור מ"ש בתורה פן תעלה עולותיך בכל מקום. היה אומר לא נאמר אלא המקריב בחוץ לעולם חייב כרת כמו שצוה משה. אבל אני אקריב היום בחוץ בדבר ה' כדי להכחיש נביאי הבעל. ועל הדרך הזאת אם צוו כל הנביאים לעבור לפי שעה מצוה לשמוע להם. ואם אמרו שהדבר נעקר לעולם מיתתו בחנק שהתורה אמרה לנו ולבנינו עד עולם:

So too, a prophet that transgresses his own instructions and the [prophet] that suppresses his prophecy, [they] are sentenced to death by the heavenly court. By all three (A regular person that does not listen to the prophet, a prophet that does not listen to himself, and a prophet that suppresses his own prophecy) it says (Devarim 18:19) "I will interrogate him." This is true even if a prophet, who is known to us to be a true prophet (he has already been proven to be a prophet), tells us to transgress one of the [613] commandments that are stated in the Torah or [if he tells us to transgress] many [commandments] regardless of whether they are easy [commandments to keep] or difficult [commandments to keep], [as long as it is only for] a finite amount of time, it is a commandment to listen to him. 

So too, we learned an oral tradition from the earlier Rabbis that, with regard to all things except idol worship, if the prophet tells us to transgress the words of the Torah, similar to how Eliyahu [transgressed commandments] by the Mount Carmel incident, we listen to him. [However,] it must be a temporary [change], similar to Eliyahu at Mount Carmel when he brought a burnt offering outside [of the Temple in Jerusalem] and [the Temple] in Jerusalem had already been chosen for [the area to bring sacrifices], and [the law states] that anyone who brings a sacrifice outside [of the Temple (once it has been designated)] is [punished] by being spiritually cut off from the nation.   [Nevertheless,] because he is a prophet it is a commandment to listen to him [even if his statements contradict the Torah in this temporary fashion] since [in a situation such as] this it states (Devarim 18:15) "You shall listen to him."

If it would have been asked to Eliyahu and said to him "How could you uproot that which is written in the Torah (Devarim 12:13) '[Do not] offer sacrifices in every place.'" He would have responded, "This commandment was only referring to one who continuously sacrifices outside [of the Temple who] will be spiritually cut off from the nation, as Moshe had commanded. However, I only brought a sacrifice today outside [of the Temple] according to the word of G-D in order to destroy the [false] prophets of the Baal." In this regard, if any of the prophets command us to transgress [a commandment other than idol worship] for a finite amount of time, it is a commandment to listen to them. [However,] if they say [a commandment] is permanently uprooted they are put to death by strangulation, since the Torah states (Devarim 29:28), "For us and our children, forever."   

One important implication we can glean from this Halacha is that a prophet that is going to change one of the commandments, even though it is only for a finite period of time, must be directly commanded by G-D to do this. As Eliyahu states (Kings 1 18:16):

וַיְהִ֣י ׀ בַּעֲל֣וֹת הַמִּנְחָ֗ה וַיִּגַּ֞שׁ אֵלִיָּ֣הוּ הַנָּבִיא֮ וַיֹּאמַר֒ יְהוָ֗ה אֱלֹהֵי֙ אַבְרָהָם֙ יִצְחָ֣ק וְיִשְׂרָאֵ֔ל הַיּ֣וֹם יִוָּדַ֗ע כִּֽי־אַתָּ֧ה אֱלֹהִ֛ים בְּיִשְׂרָאֵ֖ל וַאֲנִ֣י עַבְדֶּ֑ךָ ובדבריך [וּבִדְבָרְךָ֣] עָשִׂ֔יתִי אֵ֥ת כָּל־הַדְּבָרִ֖ים הָאֵֽלֶּה׃ 

When it was time to present the meal offering, the prophet Elijah came forward and said, “O LORD, God of Abraham, Isaac, and Israel! Let it be known today that You are God in Israel and that I am Your servant, and that I have done all these things at Your bidding.

A prophet must listen to the word of G-D and convey the message as instructed and we must follow him. However, the question arises, can a prophet infer other ideas from his prophecy or must he only repeat exactly what G-D has commanded? 

In the commentary on the Rambam named Avodat Hamelech on this Mishna it states:

ולפי דברינו יהיה כוונת רבנו לבאר דדוקא כשהנביא אומר כן בשם ה' כמו שאמר אליהו אבל אני אקריב היום בחוץ כדבר ה', משא"כ אם לא אמר כן בתורת נביא אלא בא לעשות סיג מעצמו לדבר תורה אף שהוא נביא מוחזק לא מהני ובעינן דוקא בי"ד לכך וכמ"ש בהל' ממרים

According to our words, the intention of our Rabbi (Rambam) is to explain that specifically when the prophet says [his commandment] in the name of G-D, like what Eliyahu said, "I offer this sacrifice today outside [of the Temple] according to the word of G-D." However, this is not true, [meaning we do not listen to him,] if he did not say it within the parameters of his prophecy, but rather as a way to make a fence around a Torah matter (biblical commandment) from [his own reasoning.] Even though he is an established prophet, this does not help (we do not have to listen to him), [rather,] we need the courts to [to make such a rule,] as is written [by the Rambam] in the laws of mamarim.

This is a very important point and a foundation of Jewish law. Prophets are not listened to because they are authority figures, but because they are simply repeating the word of G-D. Additionally, we only listen to them with regards to rebuke, that they are chastising us to follow the commandments, or if they tell us G-D is suspending or making an additional commandment for a FINITE amount of time. However, we DO NOT listen to a prophet to decide laws or to change any existing laws. We follow the majority of Rabbis to decide on the Torah laws. This is best illustrated in the story of the oven of Aknai where Rebbe Eliezar was arguing with the rest of the Rabbis in his day about whether the oven was pure or impure (Babba Metzia 59b):

חזר ואמר להם אם הלכה כמותי מן השמים יוכיחו יצאתה בת קול ואמרה מה לכם אצל ר"א שהלכה כמותו בכ"מ עמד רבי יהושע על רגליו ואמר (דברים ל, יב) לא בשמים היא מאי לא בשמים היא אמר רבי ירמיה שכבר נתנה תורה מהר סיני אין אנו משגיחין בבת קול שכבר כתבת בהר סיני בתורה (שמות כג, ב) אחרי רבים להטות אשכחיה רבי נתן לאליהו א"ל מאי עביד קוב"ה בההיא שעתא א"ל קא חייך ואמר נצחוני בני נצחוני בני

Rabbi Eliezer then said to them: If the halakha is in accordance with my opinion, Heaven will prove it. A Divine Voice emerged from Heaven and said: Why are you differing with Rabbi Eliezer, as the halakha is in accordance with his opinion in every place that he expresses an opinion? Rabbi Yehoshua stood on his feet and said: It is written: “It is not in heaven” (Deuteronomy 30:12). The Gemara asks: What is the relevance of the phrase “It is not in heaven” in this context? Rabbi Yirmeya says: Since the Torah was already given at Mount Sinai, we do not regard a Divine Voice, as You already wrote at Mount Sinai, in the Torah: “After a majority to incline” (Exodus 23:2). Since the majority of Rabbis disagreed with Rabbi Eliezer’s opinion, the halakha is not ruled in accordance with his opinion. The Gemara relates: Years after, Rabbi Natan encountered Elijah the prophet and said to him: What did the Holy One, Blessed be He, do at that time, when Rabbi Yehoshua issued his declaration? Elijah said to him: The Holy One, Blessed be He, smiled and said: My children have triumphed over Me; My children have triumphed over Me.   

The point of this mishna in the Rambam is to clarify how and when we are supposed to follow a prophet and when NOT to follow a prophet. 

Rambam- Yesodei HaTorah- Chapter 9 Halacha 2: One Must Follow The New Prophet As Long As He Doesn't Contradict Jewish Law

א"כ למה נאמר בתורה נביא אקים להם מקרב אחיהם כמוך. לא לעשות דת הוא בא אלא לצוות על דברי התורה ולהזהיר העם שלא יעברו עליה. כמו שאמר האחרון שבהן זכרו תורת משה עבדי. וכן אם צונו בדברי הרשות כגון לכו למקום פלוני או אל תלכו. עשו מלחמה היום או אל תעשו. בנו חומה זו או אל תבנוה. מצוה לשמוע לו והעובר על דבריו חייב מיתה בידי שמים שנאמר והיה האיש אשר לא ישמע אל 

דברי הנביא אשר ידבר בשמי אנכי אדרוש מעמו:

If it is true [that this new prophet will not change any of the laws of Judaism] then why does it say in the Torah (Devarim 18:18) "I will establish someone like you (Moshe) for the [Jewish people] from among their midst?" [G-D is] not bringing forth [a new prophet] to make a [new] religion, only to [remind the people] of the commandments of the Torah and to warn the nation not to transgress them. Like it says in [the book] of the last [prophet] (Malachi 3:22) "Remember the Torah of Moshe, my servant." Additionally, if the [prophet]commands us with regard to a matter [that the Torah does not speak about], for example go to such and such place or do not go, or wage war today or do not wage war, or build this wall or do not build it, then it is a commandment to listen to him and anyone who transgresses his command is worthy of the death penalty from Heaven, for it says (Devarim 18:19) "And it will be the man that does not listen to the [new] prophet's words that are spoken in My name, I will interrogate him."  

The Rambam now tells us the authority of the new prophet and his use. A new prophet can not erase what had been previously established, he can only add additional ancillary commandments that, according to the Rambam's examples, are for that specific time and situation. This is keeping in line with the commandment that one is neither allowed to add or subtract from the Torah (Rambam Safer Shoftim in hilchos mamarim). The Rambam continuously makes this point to show that a true Torah observant Jew could never even consider christianity or Islam as this would require someone to believe that a later prophet is coming to essentially change the previous commandments. No matter what these "prophets" do, a Torah observant Jew can not believe them. The new prophet could perform great miracles or have convincing arguments, but nothing can change the previously established commandments.

This idea brings up one of the Rambam's main ideas (Yisodei Hatorah Perek 1 Mishna 11) "[G-D] never changes, since there is nothing that can cause Him to change."  The idea that a prophet would come along and tell the Jewish people that certain commandments in the Torah are no longer to be followed would go against this basic concept of the Rambam. G-D does not change, therefore, it is impossible within the Rambam's conception of G-D that the religion that G-D created could experience any permanent change. It must be that when the Torah was initially given by Moshe, it was complete and would never be significantly altered.

The main utility of a new prophet is to remind us of the true Torah laws and that we should keep them. The additional use is that they can help guide us in matters of current events that are transient in nature like whether we need to build up protection for a future assault or if that will be seen as an aggression (build a wall or not), avoid a specific area or leave a specific area because of a future calamity (do not go to a certain place or do go), or perform a preemptive strike on an enemy or not (wage war or not). These concepts would not be found in the Torah as they are only appropriate for a specific time period and the Torah only contains that which is eternal and not bound to specific time periods. For example, war strategy against the Romans is only relevant against the Romans. Once that kingdom is gone or before they exist, there is no reason to speak of them. However, the commandments about sacrifices are relevant in any generation that has a Temple (Beis hamikdash), that is relevant in the first temple period, second temple period and it will be relevant again during the third temple period.

Breaks In Tradition, Rabbinic Authority, and The Reasons For the Commandments

In Lawrence Schiffman's "Texts and Traditions: A Source Reader for the Study of Second Temple and Rabbinic Judaism." He brings up an idea about biblical interpretation that made me think about the oral tradition and whether it was a truly unbroken chain, given down from teacher to student, from Moses until today. First, let us look at the verses in the Torah that deal with the holiday of Succos (Vayikra 23:40-43):

מ  וּלְקַחְתֶּם לָכֶם בַּיּוֹם הָרִאשׁוֹן, פְּרִי עֵץ הָדָר כַּפֹּת תְּמָרִים, וַעֲנַף עֵץ-עָבֹת, וְעַרְבֵי-נָחַל; וּשְׂמַחְתֶּם, לִפְנֵי יְהוָה אֱלֹהֵיכֶם--שִׁבְעַת יָמִים.	40 And you shall take on the first day fruit of the beautiful tree, branches of palm-trees, and leaves of thick trees, and willows of the brook, and you shall rejoice before the LORD your God seven days.
מא  וְחַגֹּתֶם אֹתוֹ חַג לַיהוָה, שִׁבְעַת יָמִים בַּשָּׁנָה:  חֻקַּת עוֹלָם לְדֹרֹתֵיכֶם, בַּחֹדֶשׁ הַשְּׁבִיעִי תָּחֹגּוּ אֹתוֹ.	41 And you shall celebrate a celebration unto the LORD seven days of the year; it is a statute forever, for generations; In the seventh month you shall celebrate it.
מב  בַּסֻּכֹּת תֵּשְׁבוּ, שִׁבְעַת יָמִים; כָּל-הָאֶזְרָח, בְּיִשְׂרָאֵל, יֵשְׁבוּ, בַּסֻּכֹּת.	42 You shall dwell in booths seven days; all that are home-born in Israel shall dwell in booths;
מג  לְמַעַן, יֵדְעוּ דֹרֹתֵיכֶם, כִּי בַסֻּכּוֹת הוֹשַׁבְתִּי אֶת-בְּנֵי יִשְׂרָאֵל, בְּהוֹצִיאִי אוֹתָם מֵאֶרֶץ מִצְרָיִם:  אֲנִי, יְהוָה אֱלֹהֵיכֶם.	43 In order that your generations may know that I made the children of Israel dwell in booths when I brought them out of the land of Egypt: I am the LORD your God.

In the current tradition, we know that verse 40 is referring to the commandment of taking the Lulav

and Esrog. Therefore, we know these verses are teaching us that on Succos we have two main commandments, the taking of the Lulav with the Esrog and dwelling in booths. However, what if the interpretation of the verses was that the booths are to be made from the four species? What if these verses were all referring to only one commandment?

This is in fact what happened in the days of Ezra and Nechemia, at the beginning of the return of the exiles, according to Lawrence Schiffman. As it states in the book of Nechemia (8:14-17):

14And they found written in the Torah that the Lord had commanded, by the hand of Moses, that the Children of Israel dwell in booths on the festival in the seventh month.		ידוַיִּמְצְאוּ כָּתוּב בַּתּוֹרָה אֲשֶׁר צִוָּה יְהֹוָה בְּיַד מֹשֶׁה אֲשֶׁר יֵשְׁבוּ בְנֵי יִשְׂרָאֵל בַּסֻּכּוֹת בֶּחָג בַּחֹדֶשׁ הַשְּׁבִיעִי:
15And that they should announce and proclaim in all their cities and in Jerusalem, saying, "Go out to the mountain and bring olive leaves and leaves of oil trees, myrtle leaves, date palm leaves, and leaves of plaited trees, to make booths, as it is written."		טווַאֲשֶׁר יַשְׁמִיעוּ וְיַעֲבִירוּ קוֹל בְּכָל עָרֵיהֶם וּבִירוּשָׁלִַם לֵאמֹר צְאוּ הָהָר וְהָבִיאוּ עֲלֵי זַיִת וַעֲלֵי עֵץ שֶׁמֶן וַעֲלֵי הֲדָס וַעֲלֵי תְמָרִים וַעֲלֵי עֵץ עָבֹת לַעֲשׂת סֻכֹּת כַּכָּתוּב:
16And the people went forth and brought [these items] and made booths for themselves, each one on his roof and in their courts and in the courts of the House of God, and in the square of the Water Gate, and in the square of the Gate of Ephraim.		טזוַיֵּצְאוּ הָעָם וַיָּבִיאוּ וַיַּעֲשׂוּ לָהֶם סֻכּוֹת אִישׁ עַל גַּגּוֹ וּבְחַצְרֹתֵיהֶם וּבְחַצְרוֹת בֵּית הָאֱלֹהִים וּבִרְחוֹב שַׁעַר הַמַּיִם וּבִרְחוֹב שַׁעַר אֶפְרָיִם:
17And all the congregation of the returnees from the captivity made booths and dwelt in the booths, for they had not done so from the days of Joshua the son of Nun until that day, and there was exceedingly great joy.		יזוַיַּעֲשׂוּ כָל הַקָּהָל הַשָּׁבִים מִן הַשְּׁבִי | סֻכּוֹת וַיֵּשְׁבוּ בַסֻּכּוֹת כִּי לֹא עָשׂוּ מִימֵי יֵשׁוּעַ בִּן נוּן כֵּן בְּנֵי יִשְׂרָאֵל עַד הַיּוֹם הַהוּא וַתְּהִי שִׂמְחָה גְּדוֹלָה מְאֹד:

First, in this story there is no mention of the lulav and esrog, which one would expect to find if they are discussing how great the observance of the holiday was. Second, in verse 15 it seems like all the materials they are gathering is only for the building of the Sukkah, not the lulav. Lastly, verse 14 uses the language of "finding," which is used when something new is discovered. Had they possessed a tradition of how to celebrate the Succos holiday, the verse would not have used the language of "finding." Therefore, the Rabbis of the time interpreted the verse as they saw fit, and that is why this holiday was, seemingly, celebrated without the commandment of lulav and esrog.

But, perhaps Lawrence Schiffman is incorrect and his analysis is off base. Nevertheless, there are other examples in the bible that appear to say the traditions of Judaism do not proceed from Moses onward in an unbroken fashion. For example, in Kings II (22:8-14) it says:

8And Hilkiah the high priest said to Shaphan the scribe, "I have found the Scroll of the Law in the house of the Lord," and Hilkiah gave the scroll to Shaphan, and he read it.		חוַיֹּאמֶר חִלְקִיָּהוּ הַכֹּהֵן הַגָּדוֹל עַל שָׁפָן הַסֹּפֵר סֵפֶר הַתּוֹרָה מָצָאתִי בְּבֵית יְהֹוָה וַיִּתֵּן חִלְקִיָּה אֶת הַסֵּפֶר אֶל שָׁפָן וַיִּקְרָאֵהוּ:
9And Shaphan the scribe came to the king and brought back word to the king, and said, "Your servants have melted the silver that was found in the Temple, and they have given it into the hands of the foremen of the work who were appointed over the house of the Lord.		טוַיָּבֹא שָׁפָן הַסֹּפֵר אֶל הַמֶּלֶךְ וַיָּשֶׁב אֶת הַמֶּלֶךְ דָּבָר וַיֹּאמֶר הִתִּיכוּ עֲבָדֶיךָ אֶת הַכֶּסֶף הַנִּמְצָא בַבַּיִת וַיִּתְּנֻהוּ עַל יַד עֹשֵֹי הַמְּלָאכָה הַמֻּפְקָדִים בֵּית יְהֹוָה:
10And Shaphan the scribe told the king, saying, "Hilkiah the priest gave me a scroll," And Shaphan read it before the king.		יוַיַּגֵּד שָׁפָן הַסֹּפֵר לַמֶּלֶךְ לֵאמֹר סֵפֶר נָתַן לִי חִלְקִיָּה הַכֹּהֵן וַיִּקְרָאֵהוּ שָׁפָן לִפְנֵי הַמֶּלֶךְ:
11And it was when the king heard the words of the scroll of the Law, that he rent his garments.		יאוַיְהִי כִּשְׁמֹעַ הַמֶּלֶךְ אֶת דִּבְרֵי סֵפֶר הַתּוֹרָה ויִּקְרַע אֶת בְּגָדָיו:

Here again we have the language of "finding" which implies that some new information was presented. However, with this source we do not need to rely upon our own interpretation. The Radak explains what happened. Radak (verse 8):

ספר התורה מצאתי בבית ה׳. דרשו כי אחז שרף את התור׳ והטמינו מפניו ספר תורה אחת והטמינוהו תחת הנדבך ועכשיו מצא חלק׳ ספר התורה הזח ורחוק הוא זה שחזקיהו שבא אחריו שרבצ תורה בישראל איך לא הוציאו וכמה ספרי תורה הניח חזקיהו במיתו אלא מנשה מלך זמן רב שהרי מלך נ״ה שנה ועשה הרע בעיני ה׳ כתועבות הגוים ובנה מזבחות לע״ג בבית ה׳ ודוא השכיח התור׳ מישראל ואין פונה אליה כי כלם היו פונים אל האלהים אחרים ואל תקית הגוים ובנ״ה שנה נשתכחה התור׳
I found a Torah scroll in the house of G-D. The [background] explanation is that Achaz burnt the Torah and one torah scroll was hidden from him, out of sight. It was hidden under stone wall (or idolatrous temple area) and now Chilkiah found this torah scroll. This incident is difficult to understand, because Chizkiyahu, who came after [Achaz] disseminated Torah throughout Israel, so how could they not find this Torah. Also, how many Torahs did Chizkiyahu leave [in the midst of Israel] when he died? Rather, Menashe ruled for a long time, he was king for 55 years, and he did such evil in the eyes of G-D, like the wicked deeds of the nations, and built alters for idol worship. He caused Israel to abandoned the Torah and they did not turn to G-D, because all of them were turning to idols and to the ways of the nations. So, after 55 years, the Torah was forgotten. 

Here, we can see the Radak claiming that the tradition from Moses had been lost. Clearly, any oral tradition or explanation of the plain meaning of the written text was not found in these days. Thus, showing a broken link in the chain of a tradition from Moses.

This break in the link of tradition is not unique to biblical sources. In the Gemara, while speaking of the tradition of which plant is the Aravos (willow-branch) it states (Sukkah 44a):

 א׳׳ל ר׳ זירא לר׳ אבהו מי א״ר יוחנן הכי והא״ר יוחנן משום ר׳ נחוניא איש בקעת בית חורתן עשר נטיעות ערבה וניסוך המים הלכה למשה מסיני אשתומם כשעה חדא ואמר שכחום וחזרו ויסדום
R. Zera to R. Abbahu, Did R. Johanan really say this? Did R. Johanan not say in the name of R. Nehunya of the Plain of Beth Hawartan that ‘the law of the ten plants, the willow-branch and the water libation were given to Moses on Mount Sinai’? [The other] was appalled for a moment and then he answered, They were forgotten and then they were re-instituted.

Rashi here states:

  שכחום. בגלות בבל שכחו את התורה והמצות במקצת וזו נשכחה לגמרי.
They were forgotten: During the exile in Babylonia they forgot part of the Torah and the commandments and this [teaching of what the Aravos were] was completely forgot.

This idea is stated in other places in the Gemara as well. The following example is a discussion of when to use the closed form vs the open form of a letter (like a mem sofit vs a regular mem) (Shabbos 104a):

לא הוה ידעין הי באמצע תיבה הי בסוף תיבה ואתו צופים תקנינהו ואכתי אלה המצות שאין הנביא רשאי לחדש דבר מעתה אלא שכחום וחזרו ויסדום
People did not know which form came in the middle of a word and which one at the end, and the Watchmen came and ordained that the open forms should be in the middle of a word and the closed forms at the end. Still, [the text states] ‘these are the commandments’, which implies that no prophet is permitted to introduce an innovation hereafter? Rather, [we must say] this law [was in fact from heaven, but] was forgotten and the Watchmen established them again.

The point of this is to show that there is no unbroken chain from Moses to us with regards to the oral Torah. In fact, there are very few laws that were given over to Moses from Sinai. That is why the Gemara only has certain laws that we say they were a Halacha L'Moshe Mi'Sinai (A law given to Moses at Sinai from G-D). The rest of the laws are derived from logical discourse of the Rabbis.

There is no better illustration of this than the story of the Oven of Aknai (Babba Metzeia 59b) where there was a dispute between Rabbi Eliezer and the Rabbis:

וזה הוא תנור של עכנאי מאי עכנאי אמר רב יהודה אמר שמואל שהקיפו דברים כעכנא זו וטמאוהו תנא באותו היום השיב רבי אליעזר כל תשובות שבעולם ולא קיבלו הימנו אמר להם אם הלכה כמותי חרוב זה יוכיח נעקר חרוב ממקומו מאה אמה ואמרי לה ארבע מאות אמה אמרו לו אין מביאין ראיה מן החרוב חזר ואמר להם אם הלכה כמותי אמת המים יוכיחו חזרו אמת המים לאחוריהם אמרו לו אין מביאין ראיה מאמת המים חזר ואמר להם אם הלכה כמותי כותלי בית המדרש יוכיחו הטו כותלי בית המדרש ליפול גער בהם רבי יהושע אמר להם אם תלמידי חכמים מנצחים זה את זה בהלכה אתם מה טיבכם לא נפלו מפני כבודו של רבי יהושע ולא זקפו מפני כבודו של ר״א ועדיין מטין ועומדין חזר ואמר להם אם הלכה כמותי מן השמים יוכיחו יצאתה בת קול ואמרה מה לכם אצל ר״א שהלכה כמותו בכ״מ עמד רבי יהושע על רגליו ואמר לא בשמים היא מאי לא בשמים היא אמר רבי ירמיה שכבר נתנה תורה מהר סיני אין אנו משגיחין בבת קול שכבר כתבת בהר סיני בתורה אחרי רבים להטות
This was the oven of 'Aknai.  Why Aknai? Rav Yehuda said in Samuel's name: [It means] that they encompassed it with arguments as a snake, and proved it unclean. It has been taught: On that day R. Eliezer brought forward every imaginable argument, but they did not accept them. He said to them: 'If the halachah agrees with me, let this carob tree prove it!' Thereupon the carob tree was torn a hundred cubits out of its place. Others say, four hundred cubits. 'No proof can be brought from a carob tree,' they retorted. Again he said to them: 'If the halachah agrees with me, let the stream of water prove it!' Whereupon the stream of water flowed backwards. 'No proof can be brought from a stream of water,' they rejoined argued. Again he urged: 'If the halachah agrees with me, let the walls of the schoolhouse prove it,' whereupon the walls inclined to fall. But R. Joshua rebuked them, saying: 'When scholars are engaged in a halachic dispute, how can you interfere?' So they did not fall, in honor of R. Joshua, nor did they resume the upright, in honour of R. Eliezer; and they are still standing this way. Again he said to them: 'If the halachah agrees with me, let it be proved from Heaven!' Whereupon a Heavenly Voice cried out: 'Why do you dispute R. Eliezer, seeing that in all matters the halachah agrees with him?!' But R. Joshua arose and exclaimed: 'It is not in heaven.' What did he mean by this? R. Jeremiah said: The Torah had already been given at Mount Sinai; we pay no attention to a Heavenly Voice, because you have already written in the Torah at Mount Sinai, After the majority must one incline.

This story teaches us something incredible, that it doesn't matter what G-D originally intended for the Halacha to be, rather it only matters how the Rabbis interpret the Torah. The tradition that we have is not an unbroken chain of what G-D said to Moses, but of the leadership of the Rabbis telling us what they think the law should be based on the written word using their logic.

This idea is not new, in fact, it is stated straight out in the bible itself (Devarim 17:9-11):

9And you shall come to the Levitic kohanim and to the judge who will be in those days, and you shall inquire, and they will tell you the words of judgment.		טוּבָאתָ אֶל הַכֹּהֲנִים הַלְוִיִּם וְאֶל הַשֹּׁפֵט אֲשֶׁר יִהְיֶה בַּיָּמִים הָהֵם וְדָרַשְׁתָּ וְהִגִּידוּ לְךָ אֵת דְּבַר הַמִּשְׁפָּט:
10And you shall do according to the word they tell you, from the place the Lord will choose, and you shall observe to do according to all they instruct you.		יוְעָשִׂיתָ עַל פִּי הַדָּבָר אֲשֶׁר יַגִּידוּ לְךָ מִן הַמָּקוֹם הַהוּא אֲשֶׁר יִבְחַר יְהֹוָה וְשָׁמַרְתָּ לַעֲשׂוֹת כְּכֹל אֲשֶׁר יוֹרוּךָ:
11According to the law they instruct you and according to the judgment they say to you, you shall do; you shall not divert from the word they tell you, either right or left.		יאעַל פִּי הַתּוֹרָה אֲשֶׁר יוֹרוּךָ וְעַל הַמִּשְׁפָּט אֲשֶׁר יֹאמְרוּ לְךָ תַּעֲשֶׂה לֹא תָסוּר מִן הַדָּבָר אֲשֶׁר יַגִּידוּ לְךָ יָמִין וּשְׂמֹאל:

Rashi on verse 11 here even tells us (from chabad.org):

either right or left,: Even if this judge tells you that right is left, and that left is right. How much more so, if he tells you that right is right, and left is left!- [Sifrei]

ימין ושמאל: אפילו אומר לך על ימין שהוא שמאל ועל שמאל שהוא ימין, וכל שכן שאומר לך על ימין ימין ועל שמאל שמאל:

To further drive home this point, I will bring in the Rambam in the Sefer HaMitzvos (312th negative commandment):

The 312th prohibition is that we are forbidden from disagreeing with the Sages who pass down the Oral Tradition (may they rest in peace), or from deviating from any of their instructions in Torah matters. The source of this prohibition is G‑d's statement (exalted be He), "Do not stray from the word that they declare to you."

And the 174th positive commandment:

The 174th mitzvah is that we are commanded to obey the Beis Din HaGadol and act in accordance with all their instructions regarding what is prohibited and what is permitted. There is no difference whether it is something they received by Oral Tradition; derived using one of the principle of Torah extrapolation; decreed in order to correct some laxity or in response to some other situation where they found it appropriate and that it would strengthen Torah observance. We are required to obey all such directives and to act in accordance with their words, not to transgress them.The source of this commandment is G‑d's statement (exalted be He), "You must keep the Torah as they interpret it for you [and follow the laws that they legislate for you]."

The Rambam is telling us that the Rabbis are the keepers of the tradition and that, although there is no unbroken chain for all the laws, there is an unbroken tradition of following the great Rabbis of the generation. Those are our leaders and they are the ones we must follow.

Still, why would G-D set up our religion in this manner? Are we not looking for the truth? Don't we want to know what G-D actually said to Moses? This setup seems to be telling us that G-D's original intention when giving the commandments to Moses is irrelevant. So then, what is the purpose of giving the Jewish people the commandments?

There is an argument in Babba Metzeia (115a) that is based on whether the commandents have reasons behind them (like to make us better people) or if they are just for us to perform because G-D told us to perform them:

 אלמנה בין שהיא ענייה בין שהיא עשירה אין ממשכנין אותה שנאמר לא תחבול  בגד אלמנה: גמ' ת״ר אלמנה בין שהיא ענייה בין שהיא עשירה אין ממשכנין אותה דברי ר׳ יהודה ר״ש אומר עשירה ממשכנין אותה ענייה אין ממשכנין אותה שאתה חייב להחזיר לה ואתה משיאה שם רע בשכנותיה למימרא דר׳ יהודה לא דריש טעמא דקרא ור״ש דריש טעמא דקרא והא איפכא שמעינן להו דתניא ולא ירבה לו נשים ר׳ יהודה אומר מרבה הוא ובלבד שלא יהו מסירות את לבו ר״ש אומר אפילו אחת והיא מסירה את לבו ה״ז לא ישאנה א״כ מה ת״ל ולא ירבה לו נשים אפילו כאביגיל לעולם ר׳ יהודה לא דריש טעמא דקרא ושאני הכא דמפרש קרא ולא ירבה לו נשים ולא יסור מאי טעמא לא ירבה לו נשים משום דלא יסור ור״ש מכדי בעלמא דרשינן טעמא דקרא לכתוב רחמנא לא ירבה ולא בעינן לא יסור ואנא ידענא מאי טעמא לא ירבה משום דלא יסור לא יסור דכתב רחמנא למה לי אפילו אחת ומסירה את לבו הרי זה לא ישאנה:
MISHNAH. A MAN MAY NOT TAKE A PLEDGE FROM A WIDOW, WHETHER SHE BE RICH OR POOR, FOR IT IS WRITTEN, THOU SHALT NOT TAKE A WIDOW'S RAIMENT TO PLEDGE. GEMARA. Our Rabbis taught: Whether a widow is rich or poor, no pledge may be taken from her: this is R. Judah's opinion. R. Simeon said: A wealthy widow we take pledges from, but not a poor one, for you are bound to return [the pledge] to her, and you bring her into disrepute among her neighbors. Now, shall we say that R. Judah does not interpret the reason of the Writ (reason for the commandments), while R. Simeon does? But we know their opinions to be the reverse. For we learned: Neither shall he multiply wives to himself, [that his heart turn not away]; R. Judah said: He may multiply [wives], providing that they do not turn his heart away. R. Simeon said: He may not take to wife even a single one who is likely to turn his heart away; what then is taught by the verse, Neither shall he multiply wives to himself? Even such as Abigail! In truth, R. Judah does not Interpret the reason of Scripture; but here it is different, because Scripture itself states the reason: Neither shall he multiply wives to himself, and his heart shall not turn away. Thus, why ‘shall he not multiply wives to himself’? So ‘that his heart turn not away.’ And R. Simeon [argues thus]: Let us consider. As a general rule, we interpret the Scriptural reason: then Scripture should have written, ‘Neither shall he multiply [etc.].’ but ‘and his heart shall not turn away’ is superfluous, for I would know myself that the reason why he must not multiply is that his heart may not turn away. Why then is ‘shall not turn away’ [explicitly] stated? To teach that he must not marry even a single one who may turn his heart.

Here, the Gemara is introducing us to a fundamental argument, do the commandments have underlying LOGICAL reasons? Rebbe Shimon believes they do and Rebbe Yehuda does not. This leads to a statement made by Rambam (The Guide for The Perplexed in Part 3 Chapter 48):

When in the Talmud (Ber. p. 33b) those are blamed who use in their prayer the phrase, "Thy mercy extendeth to young birds," it is the expression of the one of the two opinions mentioned by us, namely, that the precepts of the Law have no other reason but the Divine will. We follow the other opinion [that the Laws have reasons].

The Rambam is telling us that, as a general rule, we follow the commandments and interpret them with the idea that they have underlying reasons, not just that G-D told us to do them. This is further elucidated by the Rambam (Guide for the perplexed Part 3 Chapter 31 Friedlander translation):

 There are persons who find it difficult to give a reason for any of the commandments, and consider it right to assume that the commandments and prohibitions have no rational basis whatever...  On the contrary, the sole object of the Law is to benefit us. Thus we explained the Scriptural passage, "for our good always, that He might preserve us alive, as it is this day" (Deut. vi. 24). Again, "which shall hear all those statutes (ḥuḳḳim), and say, surely this great nation is a wise and understanding people" (ibid. iv. 6). He thus says that even every one of these "statutes" convinces all nations of the wisdom and understanding it includes. But if no reason could be found for these statutes, if they produced no advantage and removed no evil, why then should he who believes in them and follows them be wise, reasonable, and so excellent as to raise the admiration of all nations? But the truth is undoubtedly as we have said, that every one of the six hundred and thirteen precepts serves to inculcate some truth, to remove some erroneous opinion, to establish proper relations in society, to diminish evil, to train in good manners or to warn against bad habits. All this depends on three things: opinions, morals, and social conduct. We do not count words, because precepts, whether positive or negative, if they relate to speech, belong to those precepts which regulate our social conduct, or to those which spread truth, or to those which teach morals. Thus these three principles suffice for assigning a reason for every one of the Divine commandments.

 The commandments are there to make us morally, socially and emotionally better people. This is why the Rabbis are given such great power over the law, because they are supposed to guide us as to how best to understand the laws in a way that will improve us and update our morals and social constructs with an evolving society. The best example of the Rabbis doing this can be found in the Gemara in Babba Kamma (83b):

אמאי?  עין תחת עין אמר רחמנא אימא עין ממש לא סלקא דעתך דתניא יכול סימא את עינו מסמא את עינו קטע את ידו מקטע את ידו שיבר את רגלו משבר את רגלו ת״ל מכה אדם ומכה בהמה מה מכה בהמה לתשלומין אף מכה אדם לתשלומין ואם נפשך לומר הרי הוא אומר לא תקחו כופר לנפש רוצח אשר הוא רשע למות לנפש רוצח אי אתה לוקח כופר אבל אתה לוקח כופר לראשי אברים שאין חוזרין
Why [pay compensation]? Does the Divine Law not say ‘Eye for eye’? Why not take this literally to mean [putting out] the eye [of the offender]? — Let not this enter your mind, since it has been taught: You might think that where he put out his eye, the offender's eye should be put out, or where he cut off his arm, the offender's arm should be cut off, or again where he broke his leg, the offender's leg should be broken. [Not so; for the Torah] comes to teach , ‘He that smiteth any man. . .’ ‘And he that smiteth a beast . . .’ just as in the case of smiting a beast compensation is to be paid, so also in the case of smiting a man compensation is to be paid. And should this [reason] not satisfy you, note that it is stated, ‘Moreover you shall take no ransom for the life of a murderer, that is guilty of death’, implying that it is only for the life of a murderer that you may not take ‘satisfaction’, whereas you may take ‘satisfaction’ [even] for the principal limbs, though these cannot be restored.’

Here we see the Rabbis using one of the logical principles for biblical exegesis to teach that a barbaric act, taking an eye for an eye, should not be followed. They instead reinterpret the verse in a non-literal way in order to morally improve this law. This could only be done if we believe that there are reasons for the commandments, because then man can use his logic to try and figure out the reason. With the goal being moral, social and emotional improvement, that Rambam tells us, the Rabbis can then interpret the law following these guidelines.  (Also, other laws that point out this idea are multiple wives and slavery that are no longer acceptable in Judaism)

Lastly, I want to share the words of the Meiri in his Sefer Hamidos: 

Fulfilling the Mitzvos (Commandments) with the intent that they are being performed to serve the creator is sufficient for the masses and the nation. However, it is proper for individuals to try and understand all that is possible, according to their capabilities, [with regard to what are the reason for the Mitzvos]. As it says in Psalms (119:66), "Teach me good reason and knowledge; for I have believed in Your Mitzvos (commandments)." What [Psalms] means is that even though I believe in Your Mitzvos and I fulfill all of the Torah, I request to know the reason and wisdom [behind] them. This is not in order to doubt the witnesses that have testified that these Mitzvos are true, because I already believe in them. Also, my belief (emunah) does not rely on the study of these things to the extent that if I found a good connection I would believe or if I found something I considered a lie I would deny them, because this is Kefira (Heresy) and a removal of the religion completely.

The Meiri points out that the most learned of the people (aka the Rabbis) should try and understand the reasons behind the commandments. The reason for this is clear now, the Rabbis need to understand the reasons for the commandments in order for them to interpret the law appropriately. The oral tradition is based on the guiding principle that the Rabbis will lead us to a morally, socially and emotionally improved law. There is no unbroken tradition that teaches us what G-D actually said at Sinai, because it doesn't matter. Lo bashamayim hi, it is not in heaven. The Rabbis are here to guide us in the principles of Judaism through the laws that they interpret in a manner that is forever being tweaked based on our improved understanding of the reasons for the commandments. 

Rambam- Yesodei HaTorah- Chapter 9 Halacha 1: No Prophet Can Alter The Torah and G-D's Knowledge of the Future

 דבר ברור ומפורש בתורה שהיא מצוה עומדת לעולם ולעולמי עולמים אין לה לא שינוי ולא גרעון ולא תוספת שנאמר את כל הדבר אשר אנכי מצוה אתכם אותו תשמרון לעשות לא תוסף עליו ולא תגרע ממנו. ונאמר והנגלות לנו ולבנינו עד עולם לעשות את כל דברי התורה הזאת. הא למדת שכל דברי תורה מצווין אנו לעשותן עד עולם. וכן הוא אומר חוקת עולם לדורותיכם. ונאמר לא בשמים היא. הא למדת שאין נביא רשאי לחדש דבר מעתה. לפיכך אם יעמוד איש בין מן האומות בין מישראל ויעשה אות ומופת ויאמר שה' שלחו להוסיף מצוה או לגרוע מצוה או לפרש במצוה מן המצות פירוש שלא שמענו ממשה. או שאמר שאותן המצות שנצטוו בהן ישראל אינן לעולם ולדורי דורות אלא מצות לפי זמן היו. הרי זה נביא שקר שהרי בא להכחיש נבואתו של משה. ומיתתו בחנק על שהזיד לדבר בשם ה' אשר לא צוהו. שהוא ברוך שמו צוה למשה שהמצוה הזאת לנו ולבנינו עד עולם ולא איש אל ויכזב: 

It is a clear [idea] in the Torah that it (the Torah) is a [conglomeration] of commandment[s] that were established to last forever. It is not [meant] to have any changes, deletions, or additions, as it says (Devarim 13:1), "Everything I command you, be careful to do it. You shall neither add to it, nor subtract from it." It also says (Devarim 29:28), " But the revealed things are for us and our children forever: that we must fulfill all the words of this Torah." This is to teach us that all of the words of the Torah are commands for us to perform, forever. It also says (Vayikra 23:14), "An eternal statute throughout your generations." 
It also says (Devarim 30:12), "It is not in heaven." This teaches us that the prophet does not have permission to [reveal a] new [law that was not revealed previously.] Therefore, if a prophet arises from among the men of Israel or from among the nations and performs signs and wonders and then says that G-D sent him to add a commandment, to delete a commandment, to explain one of the existing commandments in a way that was not heard from Moshe, or he says the commandments that Israel were commanded to follow were not meant for the generations, but only for a specific time, this [person] is a false prophet because he is coming to contradict the prophecy of Moshe! His death penalty is strangulation because he [falsely claimed] to be speaking in the name of G-D, but he was not really commanded [by G-D.] For, [G-D] commanded Moshe that this testament (the Torah) was for us and our children for eternity and [G-D] is not like a man, who lies.    

The Rambam here is introducing us to the idea that once the Torah was given to Moshe, that is the final draft of the Torah. G-D was working on the Torah and was "tweaking it" until he finally gave it to Moshe and the Jews at Mount Sinai. However, once G-D gave the Torah, that was it. There was no more alterations, G-D wanted the Torah that was handed over to be the final draft. Any further alterations were unnecessary. Therefore, if a prophet comes and says, "G-D wanted to tweak the Torah a little more," we call him or her a liar. The reason is because the Torah was given and it is "no longer in heaven!" Man was given the perfect code.

How do we know this code was perfect and no future alterations are necessary? For starters, it was given to us by G-D. If G-D is perfect and omniscient then the code he gave us must apply for all time.  

This brings me to an interesting and very important discussion, does G-D know the future and if he does, how can there be free will?

This has been a personal struggle for me and I believe I have a decent explanation. However, first let me state the dilemma clearly. The problem is this: If G-D knows what a person will do, then how does that person have free will to perform that action? Is the person not forced into performing that action because G-D already knows it will occur?

There are three main sources to discuss if you are interested in the rationalist approach to G-D's foreknowledge. The statements made by Rabbi Akiva, the Rambam and the Ralbag. Let's start with Rabbi Akiva. 

It states in the name of Rabbi Akiva in Pirkei Avos (Ethics of our fathers, 3:15), "All is foreseen, and freedom of choice is granted." This does not help us understand anything. It is a simple statement that allows us to say that we have freedom of choice, but G-D knows everything. It seems like a contradiction, but it isn't and we must take Rabbi Akiva's word for it. This is a very unsatisfying answer. 

The Rambam gives us a little more, but not much. He bases his opinion on his approach to divine attributes (found in The Guide section 1 chapters 51-68). Basically, the Rambam says G-D's foreknowledge does not remove our freedom from our choices (See The Guide section 3 chapter 20). The reason for this is because we don't understand the idea of G-D Knowing something. G-D does not have features that are knowable. We do not have the ability to understand any attributes of G-D, therefore, we can not understand why His knowledge of events does not contradict our free will, but it does not. This answer is more detailed than Rabbi Akiva's, but it is still very unsatisfying.

The Ralbag's answer is intriguing, because he has such a unique approach to G-D's foreknowledge. He explains (In section 3 of The Wars of The Lord) that G-D does not know the future, because the future has not yet occurred, but G-D knows all of the possible outcomes based on different decisions that a person can make.

All three of these answers are difficult to take. Rabbi Akiva does not give any explanations as to why or how his statement is believable. The Rambam gives an explanation that would disallow any type of logic in Judaism, because if we can't really understand anything about G-D how can we truly understand what he said or passed down to us? Finally, the Ralbags approach would take away too much power from G-D. For, if G-D does not know the future, how can His Torah be relevant for all generations and unchangeable, like the Rambam says it is (Granted the Ralbag goes on to explain this difficulty, but the answers are still unsatisfying)?

I think the following approach makes the most sense. All of these previous approaches either lacked a way of explaining something or were the best effort for the thinking of their time. However, if we understand that space and time are finite and G-D exists outside of the finite universe, then we can understand that G-D knows everything that has occurred and everything that will occur. It is similar to watching a movie for the second time, just because I know what is going to happen in the movie, does that make the choices of the person in the movie any less of a choice? Also, it must be that G-D knows all future events in order for the Rambam's approach to be valid, because, as I stated earlier, if G-D did not know the future how could the Torah be unalterable? Obviously, the Torah would need to adjust as reality changed. However, with our approach, using a superficial understanding of space and time, we can somewhat understand how G-D's knowledge of the future works. 

Rambam-Mishna Torah Yisodei Hatora Chapter 8 Mishna 3: Why a Prophet's Miracles Do Not Prove Anything

לפיכך אם עמד הנביא ועשה אותות ומופתים גדולים ובקש להכחיש נבואתו של משה רבינו אין שומעין לו ואנו יודעין בבאור שאותן האותות בלט וכשוף הן. לפי שנבואת משה רבינו אינה על פי האותות כדי שנערוך אותות זה לאותות זה. אלא בעינינו ראינוה ובאזנינו שמענוה כמו ששמע הוא. הא למה הדבר דומה לעדים שהעידו לאדם על דבר שראה בעיניו שאינו כמו שראה שאינו שומע להן אלא יודע בודאי שהן עדי שקר. לפיכך אמרה תורה שאם בא האות והמופת לא תשמע אל דברי הנביא ההוא. שהרי זה בא אליך באות ומופת להכחיש מה שראית בעיניך והואיל ואין אנו מאמינים במופת אלא מפני המצות שצונו משה היאך נקבל מאות זה שבא להכחיש נבואתו של משה שראינו וששמענו:

Therefore, if a prophet arises and performs great wonders and miracles and tries to contradict the prophecy of Moshe, our teacher, we do not listen to him and we know with certainty that those wonders [were performed with] trickery and magic. For, the prophecy of Moshe, our teacher, was not [based] on the signs [he performed] so we could compare this sign to another [prophet's] sign. Rather, we saw with our eyes and heard with our ears like [Moshe] heard. This [prophet that is giving a prophecy that contradicts Moshe's prophecy] is similar to witnesses that testify to a man concerning something that he saw with his own eyes, [but they claim to have] seen something different than what this man saw and different from what this man heard, therefore, this man knows with certainty that these are false witnesses. Therefore, the Torah says that if a false prophet comes with signs and wonders, you should not listen to his words, because this [false prophet] is bringing you signs and wonders to contradict something that you have seen with your own eyes. And since we only believe in wonders because of the commandments that Moshe commanded us, how can we accept this sign that is being brought to contradict the prophecy of Moshe that we saw and we heard?  

The Rambam here bases this Mishna on a foundation of his philosophy. The Rambam believes that there is no such thing as an unnatural event that occurs in this world, except for those things that G-D built into creation to be unnatural. This is found in the Rambam's explanation on the Mishna in Avos (Perek 5) that speaks about the ten things that were created on the eve of Sabbath. Over there, the Rambam says that all miracles and wonders are within the realm of the natural. 

With this in mind, we can understand his stance that a prophet producing a miracle proves nothing, because this miracle is within the realm of nature. However, the Torah, G-D and Moshe's prophecy are supernatural and thus, "untouchable" by any subsequent prophet. Every miracle is a natural phenomenon and thus can not be used to overrule something supernatural that is experienced with the senses. This is why we believe in miracles only because of Moshe's prophecy, because that is what brought the supernatural into this world. Without Moshe speaking to G-D and the Jewish people witnessing it, we would not believe that anything is supernatural. 

Rambam Yesodei HaTorah Chapter 8 Halacha 2- Why There Was No Need For Moshe To Provide Miracles For People To Believe Him

נמצאו אלו ששולח להן הם העדים על נבואתו שהיא אמת ואינו צריך לעשות להן אות אחר. שהם והוא עדים בדבר כשני עדים שראו דבר אחד ביחד שכל אחד מהן עד לחבירו שהוא אומר אמת ואין אחד מהן צריך להביא ראיה לחבירו. כך משה רבינו כל ישראל עדים לו אחר מעמד הר סיני ואינו צריך לעשות להם אות. וזהו שאמר לו הקב"ה בתחילת נבואתו בעת שנתן לו האותות לעשותן במצרים ואמר לו ושמעו לקולך. ידע משה רבינו שהמאמין על פי האותות יש בלבבו דופי ומהרהר ומחשב והיה נשמט מלילך ואמר והן לא יאמינו לי. עד שהודיעו הקב"ה שאלו האותות אינן אלא עד שיצאו ממצרים ואחר שיצאו ויעמדו על ההר הזה יסתלק הרהור שמהרהרין אחריך שאני נותן לך כאן אות שידעו שאני שלחתיך באמת מתחילה ולא ישאר בלבם הרהור. והוא שהכתוב אומר וזה לך האות כי אנכי שלחתיך בהוציאך את העם ממצרים תעבדון את האלהים על ההר הזה. נמצאת אומר שכל נביא שיעמוד אחר משה רבינו אין אנו מאמינים בו מפני האות לבדו כדי שנאמר אם יעשה אות נשמע לו לכל מה שיאמר. אלא מפני המצוה שצוה משה בתורה ואמר אם נתן אות אליו תשמעון. כמו שצונו לחתוך הדבר על פי שנים עדים ואע"פ שאין אנו יודעין אם העידו אמת אם שקר. כך מצוה לשמוע מזה הנביא אע"פ שאין אנו יודעים אם האות אמת או בכישוף ולט:

We find that [the Jewish people] that [Moshe] was sent to, they were witnesses to his prophecy that it was truth and[, thus, Moshe] did not need to perform another sign for them. For [the Jewish people and Moshe] were witnesses [for his prophecy] similar to two witnesses that see an occurrence together, that both of them are witnesses that the other is speaking the truth and neither of them have to bring proof to each other. Therefore, with regards to Moshe our teacher, all of the Jewish people were witnesses for him after the events of Mt. Sinai and he did not need to perform a sign for them. 

[This idea is backed up by the conversation between G-D and Moshe by the burning bush, specifically] this that G-D said to [Moshe] at the beginning of his prophecy, at the time [G-D] was giving [Moshe] the signs that he was to perform in Egypt: And G-D said (Shemos 3:18), "They will listen to your voice." Moshe, our teacher, knew that one who believes because of a sign has fault, suspicion and suspect in his heart. [Therefore, Moshe tried to] abandon [the idea] of going and he said (Shemos 4:1), "They will not believe me." 

[Moshe pursued this course] until G-D made it known [by telling Moshe,] that these signs will only last until the [Jewish people] left Egypt. [However,] after [the Jewish people] will leave and they will stand at this mountain (Mt. Sinai) I (G-D) will remove the suspicion that they suspected after you (Moshe) for I will give you a sign here that it will be known that I sent you, in truth, from the beginning and there will not remain in their hearts any suspicion. This is what the verse [means] when it says (3:12), "This will be for you a sign that I sent you, when you take out the [Jewish] nation from Egypt you will worship G-D on this mountain."     

[The only sign that removes all doubts is that the Jewish people saw G-D speak to Moshe with their own eyes, therefore,] you will find the statement that every prophet that arose (or will arise) after Moshe, our teacher, we do not believe in him (or her) solely because of the sign [he or she performs. The reason for this is] because it would be said that if he (or she) performs a sign then we will listen to him (or her) for everything that he (or she) says. However, [the reason we believe this prophet is] because of the commandment that Moshe commanded in the Torah and said (Devarim 18:15), If a sign is given, "to him you shall listen." 

[This can be] compared to the commandment that we make a judgement by the word of two witnesses, even though we do not know if their testimony is true or false. Similarly, it is a commandment to listen to this prophet [that has a sign] even though we do not know if it is a true sign or magic and trickery." 

The Rambam here is trying to clarify his position as to how valid prophecy is and how it can be utilized. In this halacha, the Rambam is setting up the reason as to why no prophet could ever come to nullify or permanently alter the prophecy of Moshe. His point, although subtle, is that the only prophecy that can be determined to be true by others is the prophecy of Moshe. All other prophets can be lying. This is why all future prophets depend upon Moshe's prophecy and can not contradict his prophecy. This is how the Rambam can immediately brush off any claims of the Muslims or Christians.

I find the Rambam's point of view refreshing for several reasons. Mainly, the Rambam does not believe in mysticism and this idea shines through in this chapter of his Mishna Torah. The idea that one should be suspicious of anything that can not be seen with your own eyes is lacking in most circles. Only in the scientific community, and even then it is not constant, are people only swayed by empirical and reproducible evidence. An argument from authority without any tangible evidence is, according to the Rambam, inherently flawed. The sole reason that we believe Judaism is the correct religion is, simply put, because of the witnessed events at Mount Sinai. Without that single event, according to the Rambam, we would not be obligated to follow Judaism or even believe in G-D.

This point can not be over stated or overemphasized. People who claim to have prophecy or special powers and do not even produce a sign are certainly to be ignored. For, even if they had a sign we can not be sure they are telling the truth. With this as a foundation for Judaism, I think, people would stop making arguments from authority and be more open to intelligent discussions.