Numbers 3:6-9

3:6 “Bring the tribe of Levi near, and present them before Aaron the priest, that they may serve him. 3:7 They are responsible for his needs and the needs of the whole community before the tent of meeting, by attending to the service of the tabernacle. 3:8 And they are responsible for all the furnishings of the tent of meeting, and for the needs of the Israelites, as they serve in the tabernacle. 3:9 You are to assign the Levites to Aaron and his sons; they will be assigned exclusively to him out of all the Israelites.

Numbers 3:38

3:38 But those who were to camp in front of the tabernacle on the east, in front of the tent of meeting, were Moses, Aaron, and his sons. They were responsible for the needs of the sanctuary and for the needs of the Israelites, but the unauthorized person who approached was to be put to death.