That Vitamin Theory

God has landed on this enemy-occupied world in human form. And now, what was the purpose of it all? What did He come to do? Well, to teach, of course; but as soon as you look into the New Testament or any other Christian writing you will find they are constantly talking about something different--about His death and His coming to life again. It is obvious that Christians think the chief point of the story lies here. They think the main thing He came to earth to do was to suffer and be killed.

Now before I became a Christian I was under the impression that the first thing Christians had to believe was one particular theory as to what the point of this dying was. According to that theory God wanted to punish men for having deserted and joined the Great Rebel, but Christ volunteered to be punished instead, and so God let us off.[...] What I came to see later on was that neither this theory nor any other is Christianity. The central Christian belief is that Christ's death has somehow put us right with God and given us a fresh start. Theories as to how it did this are another matter. A good many different theories have been held as to how it works; what all Christians are agreed on is that it does work. I will tell you what I think it is like. All sensible people know that if you are tired and hungry a meal will do you good. But the modern theory of nourishment--about the vitamins and proteins--is a different thing. People ate their dinners and felt better long before the theory of vitamins was ever heard of: and if the theory of vitamins is some day abandoned they will go on eating their dinners just the same. Theories about Christ's death are not Christianity: they are explanations about how it works.
~C.S. Lewis, Mere Christianity, 1952