These opening years of the twentieth century have been marked by a profound revival of interest in Mysticism, though we are perhaps not yet justified in speaking of a distinct revival of Mysticism itself. This revival of interest in Mysticism can be traced to no one explanatory cause, but is due to a confluence of many contributory streams of influence. Our expanding historical knowledge has very freshly brought to light the important part which Mysticism has played in the religious life of the world, and especially in the nineteen centuries of Christian development. A group of psychological researches has aroused an immense interest in the inner life, and particularly in the deep-lying regions of the subconscious, where vast sources of hidden spiritual energy appear to lie. The prevailing tendencies in philosophy—common to many schools—to attack “intellectualism,” to humble the claims and pretensions of “knowledge,” and to exalt, on the other hand, intuition, first-hand experience, knowledge of acquaintance, appreciation, and valuation, have given aid and comfort to those who prefer the “heart” to the “head.”