No one needs, I suppose, to be told that the two chief features of Christian schematic theology are the dogmas of the Trinity and the Incarnation. They correlate and explain each other: forming together, for the Christian, the “final key” to the riddle of the world. The history of practical and institutional Christianity is the history of the attempt to exhibit their meaning in space and time. The history of mystical philosophy is the history — still incomplete — of the demonstration of their meaning in eternity.
— Evelyn Underhill, Mysticism: The Nature and
Development of Spiritual Consciousness