Why was Moshe chosen to be buried there to atone for this sin? What level in greatness did Moshe possess that was being used as the counterbalance to Pe’or?
Reb Chaim Shmuelewitz states that the idolatry of Pe’or is the attribute of wantonness. It indicates that a person has no restraint and the feelings or rights of others do not concern him. [The procedure of serving this Avodah Zarah involved defecating before the idol.] He is solely interested in himself. This is why Moshe Rabbeinu was buried opposite Pe’or. Moshe is the epithet of what it means to be interested in his task and mission of leading Klal Yisroel, and his own personal concern is the farthest thing from his mind. Moshe is the faithful servant that Hashem has complete trust in him.
This is why he can receive the “klil tiferes,” - the crown of glory on his head. A king, when he temporarily removes his crown from his head (due to its weight or on account of the heat), will not place it on the head of his vice-minister for several reasons. If someone would walk in and observe that the king’s crown is on his head, they would assume that he is indeed the king. Furthermore, the vice-minister himself would entertain those feelings. The king, therefore, would place it on a “hook on the wall.” No one will consider that the hook became king. The Holy One, Blessed be He, can place His “crown of glory” on Moshe’s head, for he is the ultimate faithful servant. Moshe will not suppose that he became the king, and nobody who sees the crown on his head will think that way.