John Chrysostom
Then he adds something else, namely that the priest receives the priesthood from another and does not appropriate it for himself. This also is common: "And no one takes this honor to himself, but he who is called by God, as Aaron was." Here he guards against another error and shows that Christ was sent by God. Christ Himself often said the same in conversation with the Jews: "I proceeded forth and came from God," and, "I have not come of Myself" (Jn 8:42). Here, it seems to me, he also alludes to the Jewish priests as untrue priests, who appropriated the rank for themselves and violated the law of the priesthood.