Numbers 18:5

2 But bring with you also your brothers from the tribe of Levi, the tribe of your father, that they may join you and assist you and your sons before the Tent of the Testimony.

3 And they shall attend to your duties and to all the duties of the Tent; but they must not come near to the furnishings of the sanctuary or the altar, or both they and you will die.

4 They are to join you and attend to the duties of the Tent of Meeting, doing all the work at the Tent; but no outsider may come near you.

5 And you shall attend to the duties of the sanctuary and of the altar, so that wrath may not fall on the Israelites again.

6 Behold, I Myself have selected your fellow Levites from the Israelites as a gift to you, dedicated to the LORD to perform the service for the Tent of Meeting.

7 But only you and your sons shall attend to your priesthood for everything concerning the altar and what is inside the veil, and you are to perform that service. I am giving you the work of the priesthood as a gift, but any outsider who comes near the sanctuary must be put to death.”

8 Then the LORD said to Aaron, “Behold, I have put you in charge of My offerings. As for all the sacred offerings of the Israelites, I have given them to you and your sons as a portion and a permanent statute.