Numbers 3:10

3:10 So you are to appoint Aaron and his sons, and they will be responsible for their priesthood; but the unauthorized person who comes near must be put to death.”

Numbers 18:3

18:3 They 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.