Numbers 18:3-6

3And 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. 4They 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.

5And you shall attend to the duties of the sanctuary and of the altar, so that wrath may not fall on the Israelites again. 6Behold, 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.