when his moral originality is greatest, when he is most certainly the organ of eternal truth. Thus understood, religious inspiration does not differ psychologically from poetic inspiration. It presents the same mystery, but it is not more miraculous. It is not produced like a trouble violently introduced into the psychical life from without, but as a really fruitful force, acting from within, in harmony with all the laws and forces of the mind. Does not experience establish and piety confirm this? When does an Amos, an Isaiah, a Jeremiah, a St. Paul, or a St. John, appear to us as the most authentic bearer of the word of truth and life, but in their most eloquent pages, where their personal genius, their faith, their thought, shine forth most freely? Religious inspiration is simply the organic penetration of man by God; but, I repeat, by an interior and indwelling God, and in such wise that when that penetration is complete, the man finds himself to be more really and fully himself than ever. It is with this mysterious action of the Spirit in the bosom of humanity as it is with the solar heat upon the plants that spring up from the soil. In regions where the heat is greatest and the other conditions favourable, plants which elsewhere are stunted attain their richest development and their greatest fecundity. The inner root of this inspiration is only found in the piety common to religious men. It differs from it not in nature, but simply in intensity and energy. Prophetic inspiration is piety raised to the second power. There is no other mystery in it than the religious mystery _par excellence_. That is why this inspiration is essential to and promotes effectually the progress of the moral and religious life. They advance together through the ages as we now shall see. CHAPTER IV THE RELIGIOUS DEVELOPMENT OF HUMANITY 1. _The Social Element in Religion_ Religion is not merely a phenomenon of the individual and inner life: it is also a social and historical phenomenon. Psychology lays bare its root, but history alone reveals its power and range.