Every high priest is selected from among the people and is appointed to represent the people in matters related to God, to offer gifts and sacrifices for sins.
“Bring Aaron and his sons, their garments, the anointing oil, the bull for the sin offering, the two rams and the basket containing bread made without yeast,
Moses said to Aaron, “Come to the altar and sacrifice your sin offering and your burnt offering and make atonement for yourself and the people; sacrifice the offering that is for the people and make atonement for them, as the Lord has commanded.”
By faith Abel brought God a better offering than Cain did. By faith he was commended as righteous, when God spoke well of his offerings. And by faith Abel still speaks, even though he is dead.
For this reason he had to be made like them, fully human in every way, in order that he might become a merciful and faithful high priest in service to God, and that he might make atonement for the sins of the people.
Unlike the other high priests, he does not need to offer sacrifices day after day, first for his own sins, and then for the sins of the people. He sacrificed for their sins once for all when he offered himself.
This is an illustration for the present time, indicating that the gifts and sacrifices being offered were not able to clear the conscience of the worshiper.