There are things, say in learning to swim or to climb, which look dangerous and aren’t. Your instructor tells you it is safe. You have good reason from past experience to trust him. Perhaps you can even see for yourself, by your own reason, that it is safe. But the crucial question is, will you be able to go on believing this when you actually see the cliff edge below you or actually feel yourself unsupported in the water?
You will have no rational grounds for disbelieving. It is your senses and your imagination that are going to attack belief. Here, as in the New Testament, the conflict is not between faith and reason but between faith and sight. We can face things which we know to be dangerous if they don’t look or sound too dangerous; our real trouble is often with things we know to be safe but which look dreadful.
Our faith in Christ wavers not so much when real arguments come against it as when it looks improbable—when the whole world takes on the desolate look which really tells us much more about the state of our passions and even our digestion than about reality.