He “has realized his guilt and will restore what he took by robbery or what he got by oppression” (v4). Most crimes or sins are double offenses; we harm other people at the same time as we offend God. Therefore, the Israelites were told to “restore” what they had stolen/broken/harmed, and “add a fifth to it” (v5), as a way of compensating the victim. They were taught to heal the broken human relationship as well as to ask for God’s forgiveness.
The Israelites were instructed to reconcile with each other on the very day they “realized their guilt” (v5). We can’t ignore human relationships and pretend to love God. He desires us to work for peace with one another.