How can we forget God's generous mercy and forgiveness to us, who are undeserving? God does not owe us forgiveness, but owes us condemnation and alienation out of justice. Instead, God casts our sins into the sea as the Psalmist says. In another place the Psalmist says that our sins are like crimson red and God will make us sterling white again with his forgiveness. While God does not remember our sins, once he forgives us, we will still remember  our hurts, even when we forgive another. But the memory of that past scar will not hold us in bondage of unforgiveness. By God's grace, and only by his grace, can we choose to forgive another, not for the other's sake, but for our sake, lest we are seen by God as an ungrateful person. Like us, the other person, from our perspective, does not deserve forgiveness, but justice and punishment. But if God has been merciful to us beyond measure, how can we deny the same things to the other? "Forgive as your heavenly Father has forgiven you."