Because according to the Christian faith, the death on the cross is the moment of victory. The divide-by-zero that absolves sin.

So, I’m no theologian, but I did grow up studying this stuff quite a bit. Here’s a probably-flawed explanation of my understanding of the teaching.

God created the world, and the creation fell short of his image for it. That’s what “sin” is, a falling-short-of-perfection. God’s perfect nature requires perfection for communion with his creation, so in an attempt to bring humanity back into communion with him, Jesus (who is both God and human) comes to live among the creation, lives a perfect life, and is killed. The teaching is that death is a result of imperfection, so the death of someone with human nature who was perfect wipes out the “cost” of sin.

So humans are again able to be connected with their Creator, despite the fact that none of them are perfect.

Christians are encouraged to follow the laws of scripture not because failure to do so will damn them, but because said laws can be good for them. The Bible outright says humans cannot get to heaven through their actions. So when Christians get all high and mighty about sin, they’re missing the point entirely. (Or, perhaps, they’re following what they’ve been taught by people who use religion to control people.)

It frustrates me to see Christians championing anti-LGBT causes and whatnot. Like, I don’t care if you think it’s sinful, the entire point of the religion is that everyone is sinful. The Bible is clear on this. Jesus came for sinners. After all, if people were perfect they wouldn’t need a savior in this system.

Someone can probably do a better, more theologically consistent job explaining this, but that’s my understanding.