Numbers 3:1 - Joseph Benson’s Commentary on the Old and New Testaments

All the other tribes being mustered and registered, and the genealogy of each stated, next follows all account of the priests and Levites, first of their descent from the two principal heads of their families; namely, Aaron and Moses; and then of the particular services allotted to each family. These Which follow in this chapter; are the generations The kindred or family. Moses's family and children are here included under the general name of the Amramites, (Numbers 3:27,) which includes all the children and grand-children of Amram, the persons only of Aaron and Moses being excepted. And the generations of Moses are thus obscurely mentioned, because they were but common Levites, the priesthood being given solely to Aaron's posterity, whence Aaron is here put before Moses, after whom he is elsewhere commonly named. In Sinai Nadab and Abihu were then alive, though dead at the time of taking this account.