Numbers 18:1-4

Then the LORD said to Aaron: “You, your sons, and your relatives from the tribe of Levi will be held responsible for any offenses related to the sanctuary. But you and your sons alone will be held responsible for violations connected with the priesthood. “Bring your relatives of the tribe of Levi—your ancestral tribe—to assist you and your sons as you perform the sacred duties in front of the Tabernacle of the Covenant. But as the Levites go about all their assigned duties at the Tabernacle, they must be careful not to go near any of the sacred objects or the altar. If they do, both you and they will die. The Levites must join you in fulfilling their responsibilities for the care and maintenance of the Tabernacle, but no unauthorized person may assist you.