This seem to be saying that G-D communicated His will directly to the people through the Cloud of Glory. When the cloud left the Mishkan that is when the Jews would break camp and start to travel, following the Cloud until it settled somewhere. That seems innocent enough, what is the difficulty?
17. and according to the cloud's departure from over the Tent, and afterwards, the children of Israel would travel, and in the place where the cloud settled, there the children of Israel would encamp. יז. וּלְפִי הֵעָלוֹת הֶעָנָן מֵעַל הָאֹהֶל וְאַחֲרֵי כֵן יִסְעוּ בְּנֵי יִשְׂרָאֵל וּבִמְקוֹם אֲשֶׁר יִשְׁכָּן שָׁם הֶעָנָן שָׁם יַחֲנוּ בְּנֵי יִשְׂרָאֵל:
18. At the bidding of the Lord, the children of Israel traveled, and at the bidding of the Lord, they encamped. As long as the cloud hovered above the Mishkan, they encamped. יח. עַל פִּי יְהֹוָה יִסְעוּ בְּנֵי יִשְׂרָאֵל וְעַל פִּי יְהֹוָה יַחֲנוּ כָּל יְמֵי אֲשֶׁר יִשְׁכֹּן הֶעָנָן עַל הַמִּשְׁכָּן יַחֲנוּ:
Well, the Cloud's departure and settling to inform the people when to travel and settle should be wholly unnecessary. This would be appropriate if there was no Moshe that could speak directly to G-D. However, Moshe spoke directly to G-D, so why could he not just tell the people when to break camp and travel? Was he not the "King" of the Jewish people at this time? Did he no longer speak with G-D "face to face?"
We can begin to understand this idea through the last verse of this (ibid 23) chapter. It says,
Somehow, the Cloud leaving and settling was an indication to travel or encamp, but these things were only done through Moshe. As Rashi tells us (ibid 18),
23. At the Lord's bidding they would encamp, and at the Lord's bidding they would travel; they kept the charge of the Lord by the word of the Lord through Moses. כג. עַל פִּי יְהֹוָה יַחֲנוּ וְעַל פִּי יְהֹוָה יִסָּעוּ אֶת מִשְׁמֶרֶת יְהֹוָה שָׁמָרוּ עַל פִּי יְהֹוָה בְּיַד משֶׁה:
At the bidding of the Lord…traveled: We learned in the [Baraitha] Melecheth HaMishkan [ch. 13]: When the Israelites traveled, the cloud would fold and spread itself over the tribe of Judah like a beam. They blew a tekiah (long blast), a teruah (series of short blasts), and another tekiah , but it (the Cloud) did not move on until Moses declared, “Rise up, O Lord” (10:35), and then the banner of the camp of Judah would travel. This [appears] in the Sifrei (84). על פי ה' יסעו: שנינו במלאכת המשכן, כיון שהיו ישראל נוסעים היה עמוד הענן מתקפל ונמשך על גבי בני יהודה כמין קורה, תקעו והריעו ותקעו ולא היה מהלך עד שמשה אומר קומה ה', ונסע דגל מחנה יהודה, זו בספרי:
and at the bidding of the Lord they encamped: As soon as the Israelites encamped, the pillar of cloud would mushroom upward and spread itself over the tribe of Judah like a canopy. It would not depart until Moses declared, “Return O Lord, to the myriads of Israel’s thousands” (10:36). This is what is meant by,“according to the Lord’s word, through Moses” (verse 23). - [Melecheth HaMishkan ch. 13]
|ועל פי ה' יחנו: כיון שהיו ישראל חונים, עמוד הענן מתמר ועולה ונמשך על גבי בני יהודה כמין סוכה, ולא היה נפרש עד שמשה אומר שובה ה' רבבות אלפי ישראל, הוי אומר על פי ה' וביד משה:|
I think the answer to this question can be seen with the stories that follow about the Jewish people's complaints. These numerous complaints in the desert can be seen starting here (Bamidbar 11:1),
This was just the first of many. For the verses show, in chapter 11, that the Jews had so many complaints to the point that Moshe cried out (ibid 11),
1. The people were looking to complain, and it was evil in the ears of the Lord. The Lord heard and His anger flared, and a fire from the Lord burned among them, consuming the extremes of the camp. א. וַיְהִי הָעָם כְּמִתְאֹנְנִים רַע בְּאָזְנֵי יְהֹוָה וַיִּשְׁמַע יְהֹוָה וַיִּחַר אַפּוֹ וַתִּבְעַר בָּם אֵשׁ יְהֹוָה וַתֹּאכַל בִּקְצֵה הַמַּחֲנֶה:
These complaints were so severe that in next week's Parsha, Shelach, we have the story of the spies. This, of course, leads to the people rejecting the thought of trying to conquer the land of Israel. In turn, the rebellion of Korach ensues. Therefore, we see a bad situation turning worse until it turns into an open rebellion.
11. Moses said to the Lord, "Why have You treated Your servant so badly? Why have I not found favor in Your eyes that You place the burden of this entire people upon me? יא. וַיֹּאמֶר משֶׁה אֶל יְהֹוָה לָמָה הֲרֵעֹתָ לְעַבְדֶּךָ וְלָמָּה לֹא מָצָתִי חסר א' חֵן בְּעֵינֶיךָ לָשׂוּם אֶת מַשָּׂא כָּל הָעָם הַזֶּה עָלָי:
However, the nature of Korach's rebellion shows us that the doubts and complaints of the Jewish people did not rest with G-D, but with Moshe. As it says (Bamidbar 16:3),
The reason for these complaints against Moshe is that Dasan and Aviram (maybe Korach as well) did not believe that Moshe was sent by G-D. This can be seen in the Dvar Torah that I wrote on Parshas Korach (found here). If this is the case, that there were still people that believed Moshe was doing somethings on his own, I believe there is a simple answer as to why the Cloud of Glory departing and resting by the word of Moshe was necessary and it did not suffice for G-D just to tell Moshe when to leave and when to camp.
3. They assembled against Moses and Aaron, and said to them, "You take too much upon yourselves, for the entire congregation are all holy, and the Lord is in their midst. So why do you raise yourselves above the Lord's assembly?" ג. וַיִּקָּהֲלוּ עַל משֶׁה וְעַל אַהֲרֹן וַיֹּאמְרוּ אֲלֵהֶם רַב לָכֶם כִּי כָל הָעֵדָה כֻּלָּם קְדשִׁים וּבְתוֹכָם יְהֹוָה וּמַדּוּעַ תִּתְנַשְּׂאוּ עַל קְהַל יְהֹוָה:
The verse in Parsha Ki Sisa (Shemos 32:9) states,
and Rashi explains that this means (from Chabad.org),
9. And the Lord said to Moses: "I have seen this people and behold! they are a stiff necked people. ט. וַיֹּאמֶר יְהֹוָה אֶל משֶׁה רָאִיתִי אֶת הָעָם הַזֶּה וְהִנֵּה עַם קְשֵׁה עֹרֶף הוּא:
The Jewish people are cynical and it is very hard for them to be convinced of the truth of something. It takes excessive amounts of proof to sway them to believe in something. However, once they believe in something it is nearly impossible to strip them of this belief. Nowadays, we look back and we see all of the Jews that gave up their lives simply because they would not convert or renounce their faith. They were stubborn in their belief in G-D because once the Jews, as a people, believe in something it is nearly impossible to expunge that belief from them.
stiff-necked: Heb. קְשֵׁה-עֹרֶף. [This is a description of stubbornness, meaning] they turned the hardness of the backs of their necks toward those who reproved them, and they refused to listen. קשה ערף: מחזרין קשי ערפם לנגד מוכיחיהם, וממאנים לשמוע:
(As a side point, I believe that this idea might have been emphasized in order to counteract people who say "people of ancient times were gullible and would believe anything." This idea counteracts that notion and shows that, at least the Jews of old, were cynical and would not just believe anything.)
This idea can be applied to the Jews in the desert as well. However, instead of being stubborn in their belief of G-D, as we see today, they were stubborn and cynical against a belief in G-D, originally. In fact, that is how G-D is referring to their stubbornness in Shemos (32:9). However, even once they were convinced of G-D's existence, they were cynical of Moshe's unwavering obedience to G-D's commands. With this in mind, I think it is fairly obvious as to why G-D felt it was necessary to have the Cloud of Glory signal, through Moshe, when the Jews should break camp and when they should encamp in different places.
The Jewish people continuously saw miracles, starting with the plagues in Egypt and culminating with the events at Mount Sinai. However, it was only on Mount Sinai that G-D spoke directly to the Jewish people and they believed, without a shadow of a doubt, in G-D's existence. Also, the only reason the people believed Moshe was sent by G-D was, simply put, because G-D told them so. Even so, G-D did not say anything about whether everything Moshe did was because G-D commanded it.
So, now that the Jews had already witnessed the events at Mount Sinai, they knew there was an all powerful G-D performing these deeds. Still, they were unsure of which commands came from G-D and which came from Moshe. Did Moshe have autonomy in certain respects or was G-D commanding everything? To solve this problem G-D made it that the Cloud of Glory, seen by everyone, would follow the word of Moshe. This symbolized that everything Moshe did was in accordance with the will of G-D. Moshe did not do anything without being commanded to do so by G-D. Every instance of breaking camp and setting up camp was only because G-D willed it.
This is also why Korach's rebellion was so devastating to Moshe. They claimed that Moshe was going against the will of G-D. This infuriated Moshe to no end because Moshe never did anything for himself, he only did things according to the will of G-D. That is why he exclaimed (Bamidbar 16:28),
This idea can also help us understand a puzzling incident, Moshe hitting the rock, that happens later in Parshas Chukas. When G-D commands Moshe to perform a miracle that will supply the Jewish people with water He says (Bamidbar 20:8),
28. Moses said, "With this you shall know that the Lord sent me to do all these deeds, for I did not devise them myself. כח. וַיֹּאמֶר משֶׁה בְּזֹאת תֵּדְעוּן כִּי יְהֹוָה שְׁלָחַנִי לַעֲשׂוֹת אֵת כָּל הַמַּעֲשִׂים הָאֵלֶּה כִּי לֹא מִלִּבִּי:
However, when Moshe actually performs the Miracle he hits the rock instead of speaking to it (ibid 11),
8. "Take the staff and assemble the congregation, you and your brother Aaron, and speak to the rock in their presence so that it will give forth its water. You shall bring forth water for them from the rock and give the congregation and their livestock to drink." ח. קַח אֶת הַמַּטֶּה וְהַקְהֵל אֶת הָעֵדָה אַתָּה וְאַהֲרֹן אָחִיךָ וְדִבַּרְתֶּם אֶל הַסֶּלַע לְעֵינֵיהֶם וְנָתַן מֵימָיו וְהוֹצֵאתָ לָהֶם מַיִם מִן הַסֶּלַע וְהִשְׁקִיתָ אֶת הָעֵדָה
This striking of the rock leads G-D to punish Moshe (ibid 12),
11. Moses raised his hand and struck the rock with his staff twice, when an abundance of water gushed forth, and the congregation and their livestock drank. יא. וַיָּרֶם משֶׁה אֶת יָדוֹ וַיַּךְ אֶת הַסֶּלַע בְּמַטֵּהוּ פַּעֲמָיִם וַיֵּצְאוּ מַיִם רַבִּים וַתֵּשְׁתְּ הָעֵדָה וּבְעִירָם:
Why such a harsh punishment for such a seemingly minor transgression? We see that G-D invested so much in Moshe. To the point that the people believed that everything Moshe did was according to the will of G-D. However, in this instance Moshe did something that was not according to the will of G-D. Therefore, G-D used this incident as a reason to tell Moshe that he could not enter the land. G-D had done everything He could in order to show the people that everything Moshe did was in accordance with G-D's will and Moshe went ahead and did something against the will of G-D. That was an extremely severe sin and it could have shaken the very foundations of faith for the Jewish people. G-D needed the people to be led into the land by someone who could make mistakes that were not directly associated with G-D.
12. The Lord said to Moses and Aaron, "Since you did not have faith in Me to sanctify Me in the eyes of the children of Israel, therefore you shall not bring this assembly to the Land which I have given them. יב. וַיֹּאמֶר יְהֹוָה אֶל משֶׁה וְאֶל אַהֲרֹן יַעַן לֹא הֶאֱמַנְתֶּם בִּי לְהַקְדִּישֵׁנִי לְעֵינֵי בְּנֵי יִשְׂרָאֵל לָכֵן לֹא תָבִיאוּ אֶת הַקָּהָל הַזֶּה אֶל הָאָרֶץ אֲשֶׁר נָתַתִּי לָהֶם:
Moshe gave us a foundation for our faith in G-D. The Jewish people, eventually, associated everything he did with the will of G-D. This required G-D to perform many actions through Moshe. However, once Moshe erred and showed that he was capable of doing something that was not in accordance with the will of G-D, it was realized that a different leader was needed to take the Jewish people to the next level, a new leader was needed to enter the land of Israel.
Returning to the original question, the Cloud of Glory was necessary because it was a continuous reminder to the Jewish people that Moshe was the direct messenger of G-D. Faith is an important thing, in order to instill faith in the "stiffnecked" people G-D needed to continuously reinforce the idea that He was communicating to them through Moshe. The Cloud of Glory was used for this purpose. In this way, Moshe was able to write the Torah and the Jewish people would believe that it was all straight from the mouth of G-D.