Of course the sinner must repent. But why? Simply because otherwise he would be unable to realise what he had done. The moment of repentance is the moment of initiation. More than that. It is the means by which one alters one's past. The Greeks thought that impossible. They often say in their gnomic aphorisms "Even the Gods cannot alter the past." Christ showed that the commonest sinner could do it. That it was the one thing he could do.
Christ, had he been asked, would have said - I feel quite certain about it - that the moment the prodigal son fell on his knees and wept he really made his having wasted his substance with harlots, and then kept swine and hungered for the husks they ate, beautiful and holy incidents in his life.
It is difficult for most people to grasp the idea. I dare say one has to go to prison to understand it. If so, it may be worthwhile going to prison.
[from De Profundis]