From Counterfeit Gods by Tim Keller
At every point in the Bible, the writers are at pains to stress that God's grace and forgiveness, while free to the recipient, are always costly for the giver. From the earliest parts of the Bible, it was understood that God could not forgive without a sacrifice. No one who is seriously wronged can "just forgive" the perpetrator. If you have been robbed of money, opportunity, or happiness, you can either make the wrongdoer pay it back or you can forgive. But when you forgive, that means you absorb the loss and the debt. You bear it yourself. All forgiveness, then, is costly.