And ye shall keep the charge of the sanctuary... — See Numbers 8:19.
Related Commentaries of Numbers 18:5
Numbers 18:5-6
5 And ye shall keep the charge of the sanctuary, and the charge of the altar: that there be no wrath any more upon the children of Israel.
6 And I, behold, I have taken your brethren the Levites from among the children of Israel: to you they are given as a gift for the LORD, to do the service of the tabernacle of the congregation.