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 almost opposites….
A great deal of our anxiety to make excuses comes from not really believing in it [forgiveness], from thinking that God will not take us to Himself again unless He is satisfied that some sort of case can be made out in our favour. But that would not be forgiveness at all. 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 has done it. That, and only that, is forgiveness, and that we can always have from God if we ask for it.
— C. S. Lewis, The Weight of Glory, quoted in A Year with C. S. Lewis, edited by Patricia S. Klein, p. 263-264