Today, Christians celebrate Easter, the biggest day on their holy calendar. It's the day that Jesus is supposed to have risen from the dead, having completed his victory over death and offering absolution from sin to all who accepted his sacrifice and followed him.
The reason for the sacrifice was to stand in the stead of all mankind to pay for their sins, which they had inherited by virtue of the sinful nature of mankind caused by the fall in Eden. On a side note, it's debatable whether or not being dead for three days and then becoming God could really be called a sacrifice, but let's leave that alone for now.
For those who believe in the literal version of Genesis, Adam and Eve were created perfectly, but some way or another, their free will managed to screw that pooch. Their disobedience (apparently God figured it was a good idea to build that in) led to sin, which led to death, decay, suffering, and struggling in life. I can't even begin to understand how a perfect being could do anything wrong, especially when it was built to be incapable of understanding right and wrong. In fact, the whole point of the fall is that Adam and Eve ate the fruit from the tree of the knowledge of good and evil, thus giving them insight into things that they could do wrong. They were punished for not knowing it was wrong to want to know right from wrong. Amazing.
For those who don't take Genesis literally, this presents a problem. If you accept evolution, for example, then there was no fall of man. There was no original sin. This could only mean that it was part of God's plan for mankind to have a sinful nature - after all, where else could it come from? Either we always had it, or we never had it at all (since there was no fall). That means that Jesus was sacrificed to pay the price for the way God made us. It's just God covering his ass, in the most ham-handed and irrational way possible - through human torture and sacrifice. Good one, Jehovah!
And if you believe in both evolution and hell, it's even worse! Not only do you think we always had a sinful nature, but you think God has a special place lined up for everybody! So God had to sacrifice himself... to himself... to make a loophole... for his own creation to escape the punishment he assigned... for behaving the way he intended us to behave from the beginning.
Ta da! Christianity makes so much sense. Good thing so few Christians actually buy into the whole 'hell' thing these days, or they might have some explaining to do - like, why their God is allowed any sort of moral authority when he punishes things for being broken that he broke himself.