There must be a sin-offering to make atonement for them. The law made them priests that had infirmity; and therefore they must first offer for their own sins, before they could make atonement for the people, Hebrews 7:27-28. They were to put their hand on the head of their sacrifice; confessing that they deserved to die for their own sins, and desiring that the killing of the beast might be accepted as a vicarious satisfaction. It was used as other sin-offerings were; only, whereas the flesh of other sin-offerings was eaten by the priests, in token of the priests taking away the sins of the people, this was appointed to be all burned without the camp, to signify the imperfection of the legal dispensation, for the sins of the priests themselves could not be taken away by those sacrifices, but they must expect a better high-priest, and a better sacrifice.
Related Commentaries of Exodus 29:10
Exodus 29:10
10 And thou shalt cause a bullock to be brought before the tabernacle of the congregation: and Aaron and his sons shall put their hands upon the head of the bullock.