Well... by the Old Testament, in Christianity it is believed that man/woman are born inheirantly evil. Yes, we get that. However, Jesus and God are forgiving, and well... most sins are considered forgiveable. The only sin that really sticks out in my mind that Jesus could not forgive was abusing and/or sexually abusing a child.

I once asked our Parish Master (Bishop), what is something that you would have to do to get into hell. He pondered for a bit, and said "Genocidals, Child Abusers, and People that refuse to ask for foregiveness."