Mysticism keeps men sane. As long as you have mystery you have health; when you destroy mystery you create morbidity.
The ordinary man has always been sane because the ordinary man has always been a mystic. He has permitted the twilight. He has always had one foot in earth and the other in fairyland. He has always left himself free to doubt his gods; but (unlike the agnostic of to-day) free also to believe in them. He has always cared more for truth than for consistency. If he saw two truths that seemed to contradict each other, he would take the two truths and the contradiction along with them. His spiritual sight is steroscopic, like his physical sight: he sees two different pictures at once and yet sees all the better for that. Thus he has always believed that there was such a thing as fate, but such a thing as free will also. Thus he believed that childeren were indeed the kingdom of heaven, but nevertheless ought to be obedient to the kingdom of earth. He admired youth because it was young and age because it was not.
It is exactly this balance of apparent contradictions that has been the whole buoyancy of the healthy man. The whole secret of mysticism is this: that man can understand everything by the help of what he does not understand.
- GK Chesterton, Orthodoxy