"Martin Luther used the phrase 'se incurvatus in se', the "self turned inward upon the self," to describe the essence of sin, and I believe he was correct in this. Unfortunately, so many modern understandings of sin are shaped by moralistic preaching and scolding, by the use of the word to justify the marginalization of those whose actions fall outside the moral codes of the upper classes, and to cover up the systemic injustices perpetrated by ostensibly upright people, that its theological richness is lost on us.
Sin is not a label to place on the shirts of bad boys and girls before sending them off to sit in the corner. It is the alienation and brokenness common to human existence, the unconquerable self-interest that makes us at once victims and victimizers, the barrier standing between ourselves and one another, which we don't even realize that we ourselves have erected. Sin is the place where Christ meets us, the place from which, one small step at a time, he liberates us, as he leads us into repentance, reconciliation with our enemies, love toward those who are not like us, solidarity with creation, and peace with a future that we cannot control.
If I can understand "sin" in this sense -- if I can acknowledge it not only when I am intentionally behaving badly toward someone else, but even when suffering brings to the surface the degree to which I am still turned inward upon myself -- then it becomes a word filled with hope. For it represents the very thing that Christ has overcome, the dimension to human existence whose power has been called into question. If I can step back and see my own self turned in upon itself, and know that that inward turn no longer represents my truest self, then I know that I am still on a journey into life."