as the Lord directed him through Moses. This was to remind the Israelites that no one except a descendant of Aaron should come to burn incense before the Lord, or he would become like Korah and his followers.
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.
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.
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.