In a recent post, I mentioned the three things that all of the major religions have in common from the Introduction to The Problem of Pain, a classic C.S. Lewis work.  They are: [1] an awareness of the numinous (or supernatural) elements existent in the universe, [2] an understanding that the moral law is written on the human heart (i.e., not learned), [3] an eventual awakening that [1] and [2] are necessarily related to each other which is another way of saying that all of the major religions deduce that God put morality in us when he made us. 

Christianity has a fourth thing which is an historical event:  the coming of a Jewish messiah, born of a virgin, and who claimed to be the son of God and also one "in being" with God.  He made a most extraordinary claim, a claim that he came to redeem us, that is, to take our sins away.  No one had ever said that before.  It is extraordinary in the sense of its universality.  What I mean by that is this:  I can forgive you if you sin against me and in some small measure redeem you, but Christ claimed that he could forgive the sins that I commit against you, that you commit against me and all other sins that are being commited and that ever will be committed to the end of the world.  The redemption in the case of Christ's forgiveness restores our friendship with God, opens the gates of heaven, and changes the world for ever.  But he had to pay a price for this universal redemption.  He not only claimed that he had to suffer brutally, and die on a cross for us, an act of unequalled love, but he did it. 

So Lewis makes the point that a person who would make such fantastic claims:  "I am God," "I forgive the sins of all," "I must die to accomplish that forgiveness," and then who in fact does die, must be either who he says he is, the God of the universe, or a raving lunatic.  Lewis posits that there can be no middle way.  He was not just a great teacher, prophet or king.  God or a madman.  Pick one.