Jewish leaders always seem to have a skeleton in their closet. Many doubted the very Jewishness of King David, the progenitor of the Moshiach, as he descends from Rut the Moavite convert. Moreover, David's entire family emanates from our forefather Yehuda's curious relationship with Tamar, his former-daughter-in-law. Ya'akov Avinu finds himself married to two sisters - a clear violation of a future Torah law. At least Moshe -- our greatest teacher -- has nothing to hide. He has impeccable family credentials - doesn't he? Actually, he doesn't.
The Torah explicitly states: "And Amram took Yocheved his aunt for a wife, and she bore him Aharon and Moshe..." (6:20) Yes, Moshe's father marries his aunt, a relationship soon to be forbidden not only to Jews, but to Noachides as well. Moshe's entire family emanates from a completely forbidden familial relationship. How can it be that our greatest teacher, and so many of our progenitors are the product of questionable family relationships?
Chizkuni comments: "The fact that God allows that a man as great as Moshe should emanate from a relationship that He would ultimately prohibit, is because we never appoint a leader over the community unless he has a 'box of vermin' hanging from his neck, lest he become haughty over his community."
Throughout his life and despite the greatness he achieves, Moshe remains the most humble man in history. Perhaps he never allows himself to forget that box hanging from his neck.