Numbers 18:3-5

Amplified Bible

³ And the Levites shall attend to your duty [as assistants] and to the duties of all the tent (tabernacle); only they shall not approach the articles of the sanctuary and the altar, or both they and you will die. ⁴ They shall join you and attend to the duties of the Tent of Meeting—all the service of the tent—and no stranger [no layman, anyone who is not a Levite] may approach you [and your sons]. ⁵ So you shall attend to the duties of the sanctuary and the duties of the altar [of burnt offering and the altar of incense], so that there will no longer be wrath on the Israelites [as with Korah, Dathan, and Abiram].^(A)