Let us suppose we possess parts of a novel or a symphony. Someone now brings us a newly discovered piece of manuscript and says, ‘This is the missing part of the work. This is the chapter on which the whole plot of the novel really turned. This is the main theme of the symphony’. Our business would be to see whether the new passage, if admitted to the central place which the discoverer claimed for it, did actually illuminate all the parts we had already seen and ‘pull them together’.
Nor should we be likely to go very far wrong. The new passage, if spurious, however attractive it looked at the first glance, would become harder and harder to reconcile with the rest of the work the longer we considered the matter. But if it were genuine then at every fresh hearing of the music or every fresh reading of the book, we should find it settling down, making itself more at home and eliciting significance from all sorts of details in the whole work which we had hitherto neglected.
Even though the new central chapter or main theme contained great difficulties in itself, we should still think it genuine provided that it continually removed difficulties elsewhere. Something like this we must do with the doctrine of the Incarnation. Here, instead of a symphony or a novel, we have the whole mass of our knowledge.
The credibility will depend on the extent to which the doctrine, if accepted, can illuminate and integrate that whole mass. It is much less important that the doctrine itself should be fully comprehensible. We believe that the sun is in the sky at midday in summer not because we can clearly see the sun (in fact, we cannot) but because we can see everything else.
From Miracles by C S Lewis