The men who initiated and guided this significant undertaking--the exhibition in the world of what they persistently called "spiritual religion"--were influenced by three great historic tendencies, all three of which were harmoniously united in their type of Christianity. They were the Mystical tendency, the Humanistic or Rational tendency, and the distinctive Faith-tendency of the Reformation. These three strands are indissolubly woven together in this type of so-called spiritual Religion. It was an impressive attempt, whether completely successful or not, to widen the sphere and scope of religion, to carry it into _the whole of life_, to ground it in the very nature of the human spirit, and to demonstrate that to be a man, possessed of full life and complete health, is to be religious, to be spiritual. I propose, as a preliminary preparation for differentiating this special type of "spiritual religion," to undertake a study, as brief as possible, of these three underlying and fundamental strands or tendencies in religion which will, of course, involve some consideration of the inherent nature of religion itself. For my present purpose it is not necessary to study the twilight history of religion in primitive races nor to trace its origins in the cradle-stage of human life. Anthropologists are rendering a valuable service in their attempts to explore the baffling region of primitive man's mind, and they have hit upon some very suggestive clues, though so far only tentative ones, to the psychological experiences and attitudes which set man's feet on the {xvi} momentous religious trail. At every stage of its long and devious history, religion has been _some sort of life-adjustment to realities which were felt to be of supreme importance either to the individual or to the race_, and it becomes thus possible for the scientific observer to note a developmental process and to discover a principle which links it in with a universal scheme of evolution.