Evelyn Underhill 
Mysticism [EPUB ebook] 
A Study in Nature and Development of Spiritual Consciousness

The most highly developed branches of the human family have in common one peculiar characteristic. They tend to produce—sporadically it is true, and often in the teeth of adverse external circumstances—a curious and definite type of personality; a type which refuses to be satisfied with that which other men call experience, and is inclined, in the words of its enemies, to "deny the world in order that it may find reality." We meet these persons in the east and the west; in the ancient, mediaeval, and modern worlds.