Numbers 18:5-7  Douay-Rheims 1899 American Edition

⁵ Watch ye in the charge of the sanctuary, and in the ministry of the altar: lest indignation rise upon the children of Israel.

⁶ I have given you your brethren the Levites from among the children of Israel, and have delivered them for a gift to the Lord, to serve in the ministries of the tabernacle.

⁷ But thou and thy sons look ye to the priesthood: and all things that pertain to the service of the altar, and that are within the veil, shall be executed by the priests. If any stranger shall approach, he shall be slain.