Josephus says, that when Moses had been brought up in the royal palaces, he was chosen as general against the Ethiopians; and having proved victorious, obtained in marriage the daughter of that king, since indeed, out of her affection for him, she delivered the city up to him.
Why was it, that when these two (Aaron and Miriam) had both acted with despite towards him (Moses), the latter alone was adjudged punishment? First, because the woman was the more culpable, since both nature and the law place the woman in a subordinate condition to the man. Or perhaps it was that Aaron was to a certain degree excusable, in consideration of his being the elder [brother], and adorned with the dignity of high priest. Then again, inasmuch as the leper was accounted by the law unclean, while at the same time the origin and foundation of the priesthood lay in Aaron, [the Lord] did not award a similar punishment to him, lest this stigma should attach itself to the entire [sacerdotal] race; but by means of his sister's [example] He awoke his fears, and taught him the same lesson. For Miriam's punishment affected him to such an extent, that no sooner did she experience it, than he entreated [Moses], who had been injured, that he would by his intercession do away with the affliction. And he did not neglect to do so, but at once poured forth his supplication. Upon this the Lord, who loves mankind, made him understand how He had not chastened her as a judge, but as a father; for He said, “If her father had spit in her face, should she not be ashamed? Let her be shut out from the camp seven days, and after that let her come in again.”
Source: Fragments from the Lost Writings of Irenaeus (New Advent)