C.S. Lewis considered George MacDonald his "master."
Alan: The following passage from C.S. Lewis' "The Silver Chair" reveals why it is not necessary to demonstrate the existence of God before making the decision to live one's life as if God existed. Generally, Lewis is somewhat too stern for me but in this passage however, he is spot on.
"I'm on Aslan's side even if there isn't any Aslan to lead it. I'm going to live as like a Narnian as I can even if there isn't any Narnia."
"The Prince and the two children were standing with their heads hung down, their cheeks flushed, their eyes half closed; the strength all gone from them; the enchantment almost complete. But Puddleglum, desperately gathering all his strength, walked over to the fire. Then he did a very brave thing. He knew it wouldn't hurt him quite as much as it would hurt a human; for his feet (which were bare) were webbed and hard and cold-blooded like a duck's. But he knew it would hurt him badly enough; and so it did. With his bare foot he stamped on the fire, grinding a large part of it into ashes on the flat hearth. And three things happened at once. First, the sweet, heavy smell grew very much less. For though the whole fire had not been put out, a good bit of it had, and what remained smelled very largely of burnt Marsh-wiggle, which is not at all an enchanting smell. This instantly made everyone's brain far clearer. The Prince and the children held up their heads again and opened their eyes. Secondly, the Witch, in a loud, terrible voice, utterly different from the sweet tones she had been using up till now, called out, "What are you doing? Dare to touch my fire again, mud-filth, and I'll turn the blood to fire inside your veins." Thirdly, the pain itself made Puddleglum's head for a moment perfectly clear and he knew exactly what he really thought. There is nothing like a good shock of pain for dissolving certain kinds of magic. "One word, Ma'am" he said coming back from the fire; limping because of the pain. "One word. All you've been saying is quite right, I shouldn't wonder. I'm a chap who always liked to know the worst and then put the best face I can on it. So I won't deny any of what you said. But there's one thing more to be said, even so. Suppose we have only dreamed, or made up, all those things - trees and grass and sun and moon and stars and Aslan himself. Suppose we have. Then all I can say is that, in that case, the made-up things seem a good deal more important than the real ones. Suppose this black pit of a kingdom of yours is the only world. Well, it strikes me as a pretty poor one. And that's a funny thing, when you come to think of it. We're just babies making up a game, if you're right. But four babies playing a game can make a play-world which licks your real world hollow. That's why I'm going to stand by the play-world. I'm on Aslan's side even if there isn't any Aslan to lead it. I'm going to live as like a Narnian as I can even if there isn't any Narnia."
The Silver Chair