These are the generations of Aaron and Moses at the time when the LORD spoke with Moses on Mount Sinai.
These are the names of the sons of Aaron: Nadab the first-born, and Abi'hu, Elea'zar, and Ith'amar; these are the names of the sons of Aaron, the anointed priests, whom he ordained to minister in the priest's office.
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.
And the LORD said to Moses, "Bring the tribe of Levi near, and set them before Aaron the priest, that they may minister to him. They shall perform duties for him and for the whole congregation before the tent of meeting, as they minister at the tabernacle; 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. And you shall give the Levites to Aaron and his sons; they are wholly given to him from among the people of Israel. 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."
And the LORD said to Moses, "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, 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."