B. Why the Jewish people are compared to the moon:

The Jewish people are compared to the moon and follow a lunar calendar. The reason for this is because just as the moon does not have any light of its own, and all of its light it receives from above, so too, the Jewish people recognize that they are completely nullified to the infinite light of G-d from whom they receive, and do not hold any independent existence. When a Jew studies Torah and performs the commands it is to be done in a way that he does not feel his independent existence, Yeish Mi Sheoheiv and Yeish Mi Shelomeid, and rather it is to be done to become nullified to G-d and become an actual abode for the infinite light of G-d.

Torah Or p. 66b-67b