What is spirit? The creative power of the Logos, in the sense in which St. John interprets and corrects the early, partial, and therefore erroneous theories of the Stoics and of Philo. God the Son, the Eternal Word of the Father, "the brightness of His glory and the figure of His Substance." "God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father: by Whom all things were made." Pure wisdom, pure will, pure energy, unconditioned by matter, but creating life out of the operation of the Holy Spirit on and through matter, and in the fullness of time becoming Incarnate for the purpose of the final redemption of man. Now since man is so compact of matter and spirit, it must follow that he cannot lay hold of pure spirit, the Absolute that lies beyond and above all material conditioning, except through the medium of matter, through its figures, its symbols, its "phantasms." Says St. Thomas: "From material things we can rise to some kind of knowledge of immaterial things, but not to the perfect knowledge thereof." The way of life therefore, is the incessant endeavour of man sacramentally to approach the Absolute through the leading of the Holy Spirit, so running parallel to the slow perfecting of matter which is being effected by the same operation. So matter itself takes on a certain sanctity, not only as something susceptible, and in process, of perfection, but as the vehicle of spirit and its tabernacle, since in matter spirit is actually incarnate. From this process follows of necessity the whole sacramental system, in theology, philosophy and operation, of Christianity. It is of its _esse;_ its great original, revolutionary and final contribution to the wisdom that man may have for his own, and it follows inevitably from the basic facts of the Incarnation and Redemption, which are also its perfect showing forth. Philosophically this is the great contribution of Christianity and for fifteen centuries it was held implicitly by Christendom, yet it was rejected, either wholly or in part, by the Protestant organizations that came out of the Reformation, and it fell into such oblivion that outside the Catholic Church it was not so much ignored or rejected as totally forgotten. Recently a series of lectures were delivered at King's College, London, by various carefully chosen authorities, all specialists in their own fields, under the general title "Mediaeval Contributions to Modern Civilization," and neither the pious author of the address on "The Religious Contribution of the Middle Ages," nor the learned author of that on "Mediaeval Philosophy," gave evidence of ever having heard of sacramental philosophy. It may be that I do them an injustice, and that they would offer as excuse the incontestible fact that Mediaevalism contributed nothing to "modern civilization," either in religion or philosophy, that it was willing to accept.