Numbers 3:6

2 These are the names of the sons of Aaron: Nadab the firstborn, then Abihu, Eleazar, and Ithamar.

3 These were Aaron’s sons, the anointed priests, who were ordained to serve as priests.

4 Nadab and Abihu, however, died in the presence of the LORD when they offered unauthorized fire before the LORD in the Wilderness of Sinai. And since they had no sons, only Eleazar and Ithamar served as priests during the lifetime of their father Aaron.

5 Then the LORD said to Moses,

6 “Bring the tribe of Levi and present them to Aaron the priest to assist him.

7 They are to perform duties for him and for the whole congregation before the Tent of Meeting, attending to the service of the tabernacle.

8 They shall take care of all the furnishings of the Tent of Meeting and fulfill obligations for the Israelites by attending to the service of the tabernacle.

9 Assign the Levites to Aaron and his sons; they have been given exclusively to him from among the Israelites.

10 So you shall appoint Aaron and his sons to carry out the duties of the priesthood; but any outsider who approaches the tabernacle must be put to death.”

Read all of Numbers 3