In the Old Testament times, people offered animals as sacrifice to receive the forgiveness of sins (Leviticus 17:11). Although it was just an animal, it was not easy for them to kill it and cut it into pieces. So, they engraved in their hearts that if they sinned someone or something would have to pay the price on their behalf. Then, they could be more careful not to commit sins. Jesus was crucified shedding blood to redeem us from our sins. If we keep it in our heart, we cannot commit sins.