And he shall lay his hand on the head of his offering and kill it at the entrance of the tent of meeting, and Aaron's sons the priests shall throw the blood against the sides of the altar.
Leviticus 3:2 ESV

Even though a peace offering is for gratitude and community, not for sin, the offerer still symbolically delegates his own life and authority to the animal through putting his hand on its head, and then he kills it himself. The only thing that God really wants from us is us. If you love him and your community, you will submit your will to his and keep his commandments.