Numbers 18:2-4

2“Bring with you your brothers, the tribe of Levi, the tribe of your father, so that they may join with you and minister to you while you and your sons with you are before the tent of the testimony.

3They must be responsible to care for you and to care for the entire tabernacle. However, they must not come near the furnishings of the sanctuary and the altar, or both they and you will die.

4They must join with you, and they will be responsible for the care of the tent of meeting, for all the service of the tent, but no unauthorized person may approach you.