On these grounds and others like them one is driven to think that whatever else may be true, the popular scientific cosmology at any rate is certainly not. I left that ship not at the call of poetry but because I thought it could not keep afloat. Something like philosophical idealism or Theism must, at the very worst, be less untrue than that. And idealism turned out, when you took it seriously, to be disguised Theism. And once you accepted Theism, you could not ignore the claims of Christ. And when you examined them it appeared to me that you could adopt no middle position. Either He was a lunatic, or God. And He was not a lunatic.
I was taught at school, when I had done a sum, to “prove my answer.” The proof or verification of my Christian answer to the cosmic sum is this. When I accept Theology I may find difficulties, at this point or that, in harmonising it with some particular truths which are imbedded in the mythical cosmology derived from science. But I can get in, or allow for, science as a whole. Granted that Reason is prior to matter and that the light of the primal Reason illuminates finite minds, I can understand how men should come, by observation and inference, to know a lot about the universe they live in. If, on the other hand, I swallow the scientific cosmology as a whole, then not only can I not fit in Christianity, but I cannot even fit in science. If minds are wholly dependent on brains, and brains on biochemistry, and biochemistry (in the long run) on the meaningless flux of the atoms, I cannot understand how the thought of those minds should have any more significance than the sound of the wind in the trees. And this is to me the final test. This is how I distinguish dreaming and waking. When I am awake I can, in some degree, account for and study my dream. The dragon that pursued me last night can be fitted into my waking world. I know that there are such things as dreams; I know that I had eaten an indigestible dinner; I know that a man of my reading might be expected to dream of dragons. But while in the nightmare I could not have fitted in my waking experience. The waking world is judged more real because it can thus contain the dreaming world; the dreaming world is judged less real because it cannot contain the waking one. For the same reason I am certain that in passing from the scientific points of view to the theological, I have passed from dream to waking. Christian theology can fit in science, art, morality, and the sub-Christian religions. The scientific point of view cannot fit in any of these things, not even science itself. I believe in Christianity as I believe that the Sun has risen, not only because I see it, but because by it I see everything else.
–C.S.Lewis, The Weight of Glory: “Is Theology Poetry?” (Harper Collins 2001 edition) pages 139-140, emphasis mine