Numbers 18:5
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. 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.
Aaron and his sons were charged with keeping the sanctuary and the altar in their appointed priestly service. Their guarding oversight was the appointed means to keep divine wrath from falling upon the Israelites. The sacred duties, boundaries, and divine appointments of the sanctuary were to be faithfully maintained only by those whom God had assigned to them.
The priests alone were to minister before God and to offer sacrifices. The other Levites were to assist them and to care for the tabernacle and its furnishings. They were not to perform priestly rites, nor to look upon the holy things until they had been covered. This faithful keeping of the charge of the sanctuary and the altar was to prevent wrath from coming any more upon Israel through improper approach or service.