Moses numbered them - Though Moses and Aaron conjointly numbered the twelve tribes, yet Moses alone numbered the Levites; "for as the money with which the first-born of Israel, who exceeded the number of Levites, were redeemed, was to be paid to Aaron and his sons, Numbers 3:48, it was decent that he, whose advantage it was that the number of the first-born of Israel should exceed, should not be authorized to take that number himself." - Dodd, from Bishop Kidder.

And Moses numbered them according to the word of the Lord,.... Took the account of all of a month old in the several houses and families of the tribe of Levi; though Moses is only here mentioned, yet it seems from Numbers 3:39; that Aaron was concerned with him in it; yea, in an after numbering of the Levites who were fit for business from thirty to fifty years of age, the chief of the children of Israel were assisting to him and Aaron, Numbers 4:46,
as he commanded; he was obedient to the divine will in all things, and so in this, though it was his own tribe and his own posterity, which in all successive ages were to be no other than ministering servants to the priests, and to have no inheritance in the land of Israel.