"Real forgiveness means looking steadily at the sin, the sin that is left over without any excuse, after all allowances have been made, and seeing it in all its horror, dirt, meanness, and malice, and nevertheless being wholly reconciled to the man who had done it. That, and only that, is forgiveness, and that we can always have from God if we ask for it."
I'm not sure we often think of forgiveness like this; it would mean conceding that we are indeed dirty, mean, and malicious. We prefer excuses. But Lewis' definition of real forgiveness is worth extended reflection. We see most clearly the surprising beauty of the cross in those moments when we are most honest about the darkness of the filth of our rebel hearts. God will never excuse our offense against him; he will however forgive it. He doesn't look the other way. He takes it head on. In the cross he takes upon himself (himself!) the horror and pain of our transgression against him. The Holy One looks steadily at our sin and chooses not to hold it against us. Stunning. Absolutely stunning.
This is what God has done for us in Christ, it is likewise what he calls upon us to do. Imitate him. So, Lewis: "To be a Christian means to forgive the inexcusable, because God has forgiven the inexcusable in you." He continues:
"This is hard. It is perhaps not so hard to forgive a single great injury. But to forgive the incessant provocations of daily life - to keep forgiving the bossy mother-in-law, the bullying husband, the nagging wife, the selfish daughter, the deceitful son - how can we do it? Only, I think, by remembering where we stand, by meaning our words when we say in our prayers each night 'forgive us our trespasses as we forgive those that trespass against us.' We are offered forgiveness on no other terms."
It is nearly impossible to become a forgiving person until one finds himself a forgiven person. One cannot be like God without first being reconciled to God.