"Mysticism is religion, and supplies a refuge for men of religious minds who find it no longer possible for them to rest on 'external authority'—as George Tyrrell both expounded and illustrated for us. Once turn away from revelation and little choice remains to you but the choice between Mysticism and Rationalism. There is not so much choice between these things, it is true, as enthusiasts on either side are apt to image. The difference between them is very much a matter of temperament, or perhaps we may even say of temperature. The Mystic blows hot, the Rationalist cold. Warm up a Rationalist and you inevitably get a Mystic; chill down a Mystic and you find yourself with a Rationalist on your hands. The history of thought illustrates repeatedly the easy passage from one to the other. Each centers himself in himself, and the human self is not so big that it makes any large difference where within yourself you take your center. Nevertheless just because Mysticism blows hot, its 'eccentricity' is the more attractive to men of lively religious feeling."
—Benjamin B. Warfield, in the "Princeton Theological Review."