Ramban on the Reason for Mitzvos

The Ramban speaks extensively on the reason for the commandments in Parshas Ki Saitzay (Devarim 22:6). He says that the reason for the commandment of Shiluach Hakan (sending away the mother bird before taking the eggs) was given in order that man not be cruel. Also, the reason for not being able to slaughter an animal on the same day as its child (Vayikra 22:28) is so that a person should not be cruel. What is the Ramban trying to tell us here? According to the Ramban, what, precisely, is the reason for all the commandments. These specific reasons are easy to see, but what is the underlying basis for all the commandments? What one idea will be able to explain all the commandments?

The Maharal explains that the Ramban is saying that the commandments were given for our, man's, benefit. Their purpose is to refine man and to purify him like pure silver. The commandments are not for the benefit of G-D or to be merciful to animals, but rather they are to keep harm, evil beliefs, or bad character traits away from man in order that man's soul be cleansed and brought to completeness. The whole reason for the commandments is so that man should stay away from wicked characteristics like cruelty, but they have nothing to do with having mercy on animals and the like, rather they are guidelines of how to reach good character traits which ultimately lead us to the correct path of life.