Numbers 3:1

These also are the generations of Aaron and Moses— As the posterity of Aaron only is mentioned, some have thought that generations here signifies, not only posterity, but acts, passages of their history, or what happened to them; as the word is used, Genesis 2:4; Genesis 6:9. Le Clerc is of opinion, that Aaron is mentioned first, as being the elder brother, and on that account having the priesthood attached to his posterity; whereas the posterity of Moses were numbered only among the common Levites: and he thinks that one reason for excluding the sons of Moses from the priesthood, was their not being born of an Israelitish mother; see Exodus 2:21. The words, "In the day that the Lord spake with Moses in mount Sinai," seem to be added, because at that time Nadab and Abihu were both alive, though now dead at this numbering of the Levites. The disinterestedness of Moses, in making no provision for his own immediate descendants, is an evident proof of the Divinity of his mission.