Original Sin

Original Sin is a fundamental concept of Christianity. It is an idea that distinguishes the religion from the other two Abrahamic faiths.

All three Abrahamic faiths believe that when Adam and Eve fell by disobeying God's order not to eat the fruit of the tree of the knowledge of good and evil, they rendered the Creation imperfect, introducing sin, pain and death into the world. For this they were punished by being expelled from the Garden of Eden. Christians hold that in addition, the guilt of their original sin is passed on to all humans: that from the moment of birth, humans are already distanced from God by being in a state of sin. (This is why a baby is baptized - the taint of Original Sin is washed away in a religious ceremony.)

The importance of Original Sin in Christianity is that Jesus is seen as the remedy for it: God sent "His only Son" into the world so that, by His death, the sin of Adam is purged, or redeemed. The point is made by Saint Paul in I Corinthians ch. 15, v. 8: "For since by man [Adam] came death, by man [Jesus] came also the resurrection of the dead. For as in Adam all die, even so in Christ shall all be made alive."

(Different Christian sects hold slightly different versions of the doctrine laid out in a simple form here.)