It's about Christianity

"I started to learn that everything that's considered a sin is what makes you a human being. All the seven deadly sins are man's true nature—to be greedy, to be hateful, to have lust. Of course you have to control them; but if you're made to feel guilty for being human, then you're going to be trapped in a never-ending sin-and-repent cycle that you can't escape from, and you're going to be miserable. Ultimately you'll be living in your own hell. So there's no need to worry about going to hell, because hell will be on earth.."

-Marilyn Manson


All the characters in this film desperately want to feel that they are accepted. Stone says so explicitly when he challenges Jack's role of judging him. I should add that Jack is somewhat like God: he stands in final judgment of sinners. But getting back to the acceptance theme, we see that Lucetta gains her acceptance sexually; she just wants to sleep with men because that's her mechanism for feeling accepted. That's why she calls over the guy in the beginning of the film for a quick lay, and that's why she pleads with Jack to stay in touch even when Stone gets release----she's so insecure and scared of not being accepted that she can't even let Jack out her life (regardless of how he came into it). This is why Stone is liberated by the end of the film when he speaks about the fact that he did not feel guilt during the offenses that lead him to jail. Simply put, Stone has accepted himself for better or worse.

The ultimate irony of Christianity is that its predicated upon forgiveness. But when sin is equivalent to human nature, then everyone will continue to sin, and therefore forgiveness can never be permanent. It only lasts until the individual inevitably sins again. Learning to accept that cycle is what liberates Stone. Jack cannot see that; he screams at Stone at the end that all the convicts are the same and they never change. Jack does not realize that whether one changes or not is actually beside the point; the emphasis, instead, should be on whether one learns from those mistakes and accepts those mistakes instead of hating oneself for making those mistakes.