When we come to man, the highest of the animals, we get the completest resemblance to God which we know of. (There may be creatures in other worlds who are more like God than man is, but we do not know about them.) Man not only lives, but loves and reasons: biological life reaches its highest known level in him.
But what man, in his natural condition, has not got, is Spiritual life—the higher and different sort of life that exists in God. We use the same word life for both: but if you thought that both must therefore be the same sort of thing, that would be like thinking that the ‘greatness’ of space and the ‘greatness’ of God were the same sort of greatness. In reality, the difference between Biological life and Spiritual life is so important that I am going to give them two distinct names. The Biological sort which comes to us through Nature, and which (like everything else in Nature) is always tending to rundown and decay so that it can only be kept up by incessant subsidies from Nature in the form of air, water, food, etc., is Bios. The Spiritual life which is in God from all eternity, and which made the whole natural universe, is Zoe. Bios has, to be sure, a certain shadowy or symbolic resemblance to Zoe: but only the sort of resemblance there is between a photo and a place, or a statue and a man. A man who changed from haying Bios to having Zoe would have gone through as big a change as a statue which changed from being a carved stone to being a real man.
And that is precisely what Christianity is about. This world is a great sculptor’s shop. We are the statues and there is a rumour going round the shop that some of us are some day going to come to life.
C.S. Lewis, Mere Christianity (1952; Harper Collins: 2001) 158-159.