Numbers 3:1-13 Revised Standard Version (RSV)
The Sons of Aaron
3 These are the generations of Aaron and Moses at the time when the Lord spoke with Moses on Mount Sinai. 2 These are the names of the sons of Aaron: Nadab the first-born, and Abi′hu, Elea′zar, and Ith′amar; 3 these are the names of the sons of Aaron, the anointed priests, whom he ordained to minister in the priest’s office. 4 But Nadab and Abi′hu died before the Lord when they offered unholy fire before the Lord in the wilderness of Sinai; and they had no children. So Elea′zar and Ith′amar served as priests in the lifetime of Aaron their father.
The Duties of the Levites
5 And the Lord said to Moses, 6 “Bring the tribe of Levi near, and set them before Aaron the priest, that they may minister to him. 7 They shall perform duties for him and for the whole congregation before the tent of meeting, as they minister at the tabernacle; 8 they shall have charge of all the furnishings of the tent of meeting, and attend to the duties for the people of Israel as they minister at the tabernacle. 9 And you shall give the Levites to Aaron and his sons; they are wholly given to him from among the people of Israel. 10 And you shall appoint Aaron and his sons, and they shall attend to their priesthood; but if any one else comes near, he shall be put to death.”
11 And the Lord said to Moses, 12 “Behold, I have taken the Levites from among the people of Israel instead of every first-born that opens the womb among the people of Israel. The Levites shall be mine, 13 for all the first-born are mine; on the day that I slew all the first-born in the land of Egypt, I consecrated for my own all the first-born in Israel, both of man and of beast; they shall be mine: I am the Lord.”