God appointed Aaron, the brother of Moses, to be the first high priest of the Jewish nation. After Moses followed God’s instructions in anointing Aaron and his sons, Aaron was then able to offer the prescribed sacrifices to God, Everything offered had to be without blemish or the sacrifice was not acceptable. These were offered on the altar and when they were offered properly, God would accept them as a sweet smelling sacrifice and forgive the sins of the people. Aaron understood the weakness of the people and their inability to refrain from disobedience. He suffered from the same weakness. (Read Exodus 32 for that story). So he could have empathy and compassion on the people as he offered the sacrifices for both his and their sins. This was a temporary fix that God allowed until a true sacrifice could be given.There is no remission of sin without the shedding of blood, Since sin came into the world through the disobedience of the first man, Adam, complete permanent remission of sin would have to wait on the sacrifice of a perfect man.