Then the Lord said to Moses, “Come up to the Lord, you and Aaron, Nadab and Abihu, and seventy of the elders of Israel. You are to worship at a distance,
and fasten caps on them. Then tie sashes on Aaron and his sons. The priesthood is theirs by a lasting ordinance. “Then you shall ordain Aaron and his sons.
Moses said to Aaron and his remaining sons, Eleazar and Ithamar, “Take the grain offering left over from the food offerings prepared without yeast and presented to the Lord and eat it beside the altar, for it is most holy.
But only you and your sons may serve as priests in connection with everything at the altar and inside the curtain. I am giving you the service of the priesthood as a gift. Anyone else who comes near the sanctuary is to be put to death.”
Nadab and Abihu, however, died before the Lord when they made an offering with unauthorized fire before him in the Desert of Sinai. They had no sons, so Eleazar and Ithamar served as priests during the lifetime of their father Aaron.