In religion, a sacrifice is the killing of an animal or human being to please gods or goddesses.
Some religions like the Azteks believed that the gods required human beings to die in horrifiying ways, such as getting their hearts ripped open. Another ancient Latin American civilization, the Incans, sacrificed their children by putting them high into the mountains, where they froze and became mummies.
In Christianity, animals were sacrificed because humans are better then animals. This stopped when Jesus "sacrificed" himself, because that was supposedly the ultimate sacrifice, but that makes no sense, since people are still sinners.
There is another weird thing about Jesus on the cross. While fundies have no problem with the idea of a literal garden of Eden, more educated Christians regard it as a myth or an allegory. However one of the reasons given by all Christians for Jesus' death on the cross is to atone for original sin. Now if the story of the snake and the tree and all is a myth - why did god decide to torture himself to make up for this myth?
A: because he's a weirdy