Numbers 18:1-4

The LORD said to Aaron, “You, your sons and your family are to bear the responsibility for offenses connected with the sanctuary, and you and your sons alone are to bear the responsibility for offenses connected with the priesthood. Bring your fellow Levites from your ancestral tribe to join you and assist you when you and your sons minister before the tent of the covenant law. They are to be responsible to you and are to perform all the duties of the tent, but they must not go near the furnishings of the sanctuary or the altar. Otherwise both they and you will die. They are to join you and be responsible for the care of the tent of meeting—all the work at the tent—and no one else may come near where you are.