Numbers 26:57

57.And these are they that were numbered of the Levites. He treats separately of the tribe of Levi, which God had dissevered from the rest of the people; and of the sons of Levi, the last mentioned is Kohath, the founder of the sacerdotal family. Hence we may probably conjecture that the law of primogeniture was not regarded when God deigned to take the priests from thence. But why Moses should expressly state the name of his mother, contrary to the usual custom of Scripture, does not dearly appear; for it is not likely that he did this as a distinction to his own family, because he at the same time shews how he himself, as well as his children, was deprived of the honor (of the priesthood,) (196) in which certainly there is no appearance of ambition. It is more probable, if the word daughter is literally taken, that he did not conceal a disgraceful circumstance, in order to extol more highly the indulgence of God; for, in this case, Moses and Aaron sprang of an incestuous marriage, since Amram, their father, must have married his aunt, which natural modesty forbade. It will, then, be rather an ingenuous confession of family dishonor, than an ambitious boast. If we inquire how this could have been tolerated, the answer will readily suggest itself, that this license had so largely prevailed among the oriental nations, that no one deemed that to be illicit which was in such universal use. And this we shall presently see (197) to be expressly referred to, when God, by forbidding incestuous marriages, distinguishes His people from other nations. It will be no matter of surprise, then, that those who were not yet prohibited from doing so by the law of God, had followed the general custom.