In setting up his explanation for how he came to an orthodox faith in God, Chesterton describes the materialist who relies ultimately on logic as a mad person. One example is that a mad person might claim to be God--and the way one would work with such a person is not to deny that they are God but to point out that if they are indeed the creator of the universe, then what a small and insignificant universe it must be. Similarly, a non Christian who is worried that all truth claims meet the rule of logic limit truth possibilities to a small circle. The basic argument, which is too complicated for me to work out in a blog, is something along the lines that Christianity is more creative, less limited, and therefore more sane than materialistic rationality.
Spiritual doctrines do not actually limit the mind as do materialistic denials. Even if I believe in immortality I need not think about it. But if I disbelieve in immortality I must not think about it. In the first case the road is open and I can go as far as I like, but in the second, the road is shut.
Chesterton's argument is not that the rational skeptic is not rational--rather rational skepticism is infinitely rational, it just happens to be a small and limited infinity. "Their position is quite reasonable, nay, it is infinitely reasonable, just as a threepenny is infinitely circular... [it is] a base and slavish eternity."
All this is to set up what I believe to be the best use of the image of the cross that I have ever encountered.
For the circle is perfect and infinite in its nature; but it is fixed forever in its size; it can never be larger or smaller. But the cross, though it has at its heart a collision and a contradiction, can extend its four arms forever without altering its shape. Because it has a paradox at its center, it can grow without changing.
This image of the cross having a collision and paradox at its center is why we can know things to be true that may not fit our limited reason. Like, "The one who loses their life for my sake will find it." This is not a rational statement, but in the cross it makes sense. Which is true that God is sovereign over all and knows everything before it happens or that God has given humans free will--they are both true. Sure it is paradoxical but it can be the case in the cross. Do we seek righteousness or surround ourselves with sinners--both, are we holy or imperfect--both are true, that is the shape of the cross.
"The morbid logician seeks to make everything lucid, and succeeds in making everything mysterious. The mystic allows one thing to be mysterious, and everything becomes lucid." I love this image.