What is the point of a crucifix? It's supposed to remind us of the good news, that Jesus saved us from sin, right? But wait, aren't we all still sinners in the eyes of God? So what does it mean that Jesus saved us? Supposedly, Jesus saved us from an eternity of hellfire by acting as an intermediary between us and God, introducing the concept of forgiveness (suggesting the omniscient one didn't already know about it).
Forgiveness for what exactly though? The answer we're given is that we require forgiveness not so much for what we've done but for what we are. This is the concept of original sin. In effect, we're all guilty at birth because Adam and Eve ate the fruit of the tree of knowledge of good and evil. The original pair were disobedient, so Jesus had to be tortured and crucified, and it's all our fault.
The response of many to criticism of the old testament as profoundly immoral--misogyny, infanticide, genocide, etc--is that the new testament is in fact the basis of Christian morality. But this isn't much of a defense. The new testament is the height of sadomasochistic hokeyiness. It doesn't hold up to even the flimsiest test of logic.
In practical terms, though, the message is quite effective. As little catholic boys and girls we were told again and again the good (?) news that Jesus died for our sins. So we were to believe that as six- and seven-year-olds we had behaved so abominably that someone had to undergo torture and death to make amends. Of course, Jesus is dead, sort of, and so we can't repay our life debt to him. Instead, we owe our lives, by an accounting of simple reciprocity, to the institution that represents him, the church.
My ex-girlfriend often told me that I had ruined her life; the corollary would be that I owed her my life in return. She owned me. This is how guilt trips function. People have an innate capacity to harbor feelings of guilt and unworthiness that are ready-made for this type of exploitation. This basic manipulativeness, and not any element of truth, is most likely what accounts for the staying power of Christianity relative to other religions.