Charles Ellicott Commentary Numbers 3:10

"And thou shalt appoint Aaron and his sons, and they shall keep their priesthood: and the stranger that cometh nigh shall be put to death." — Numbers 3:10 (ASV)

Thou shalt appoint. —Or, number. The word is the same as the one used for the numbering of the Israelites generally (Numbers 1:19) and for the numbering of the Levites (Numbers 3:15).