I find that when I think I am asking God to forgive me I am often in reality (unless I watch myself very carefully) asking Him to do something quite different. I am asking Him not to forgive me but to excuse me. But there is all the difference in the world between forgiving and excusing. Forgiveness says “Yes, you have done this thing, but I accept your apology; I will never hold it against you and everything between us two will be exactly as it was before”. But excusing says “I see that you couldn’t help it or didn’t mean it; you weren’t really to blame.” If one was not really to blame then there is nothing to forgive. In that sense forgiveness and excusing are opposites… If you had a perfect excuse, you would not need forgiveness; if the whole of your action needs forgiveness, then there was no excuse for it. But the trouble is that what we call “asking God’s forgiveness” very often really consists in asking God to accept our excuses. What leads us into this mistake is that the fact that there usually is some amount of excuse, some “extenuating circumstances.” We are so very anxious to point these out to God (and to ourselves) that we are apt to forget the really important thing; that is the bit left over, the bit which the excuses don’t cover, the bit which is inexcusable but not, thank God, unforgivable. And if we forget this, we shall go away imagining that we have repented and been forgiven when all that has really happened is that we have satisfied ourselves with our own excuses. They may be very bad excuses; we are all to easily satisfied about ourselves.
There are two remedies for this danger. One is to remember that God knows all the real excuses very much better than we do… The second remedy is really and truly to believe in the forgiveness of sins… 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 malic, and nevertheless being wholly reconciled to the man who has done it. That, and only that, is forgiveness, and that we can always have from God if we ask for it.
-An excerpt from “The Weight of Glory”, C. S. Lewis ISBN 978-0-06-065320-0 pp178-180