Numbers 18:1
And the LORD said unto Aaron, Thou and thy sons and thy father’s house with thee shall bear the iniquity of the sanctuary: and thou and thy sons with thee shall bear the iniquity of your priesthood. And the LORD said unto Aaron, Thou and thy sons and thy father’s house with thee shall bear the iniquity of the sanctuary: and thou and thy sons with thee shall bear the iniquity of your priesthood.
The Lord placed responsibility for the sanctuary upon Aaron together with his sons and his father's house with him, and responsibility for the priesthood upon Aaron with his sons. To bear the iniquity of the sanctuary and of the priesthood is to be accountable for guarding the sanctuary and the altar and for carrying out its sacred service, keeping the appointed charge so that no wrath falls upon Israel. That priestly service was to be performed at the altar and within the veil. The priestly office itself was bestowed as a service.
The priesthood belonged to Aaron's family alone, while the other Levites were to care for the tabernacle and its furnishings and to assist the priests. They were not to offer sacrifice or burn incense, nor to look upon the holy things before they were covered. Any unauthorized person who approached the priestly service was to be put to death. Each worker was therefore to faithfully perform his own assigned duties without taking up another's work.