Suppose someone asked me, when I see a man in blue uniform going down the street leaving little paper packets at each house, why I suppose that they contain letters? I should reply, ‘Because when ever he leaves a similar little packet for me I find it does contain a letter.’ And if he then objected—’But you’ve never seen all these letters which you think the other people are getting,’ I should say, ‘Of course not, and I shouldn’t expect to, because they’re not addressed to me. I’m explaining the packets I’m not allowed to open by the ones I am allowed to open.’ It is the same about this question. The only packet I am allowed to open is Man. When I do, especially when I open that particular man called Myself, I find that I do not exist on my own, that I am under a law; that somebody or something wants me to behave in a certain way. I do not, of course, think that if I could get inside a stone or a tree I should find exactly the same thing, just as I do not think all the other people in the street get the same letters as I do. I should expect, for instance, to find that the stone had to obey the law of gravity—that whereas the sender of the letters merely tells me to obey the law of my human nature, he compels the stone to obey the laws of its stony nature. But I should expect to find that there was, so to speak, a sender of letters in both cases, a Power behind the facts, a Director, a Guide.
Quotes from Mere Christianity, Part 10
C.S. Lewis, Mere Christianity (1952, this edition: 2001) 24-25.