truth which has for a generation past grown in men's apprehension that there is no possibility of understanding Christianity, except against the background of the religious life and thought of the world into which it came. Christianity had vital relation, at every step of its progress, to the religious movements and impulses of the ancient world, especially in those centres of civilisation which Paul singled out for his endeavour and which remained the centres of the Christian growth. It was an age which has often been summarily described as corrupt. Despite its corruption, or possibly because it was corrupt, it gives evidence, however, of religious stirring, of strong ethical reaction, of spiritual endeavour rarely paralleled. In the Roman Empire everything travelled. Religions travelled. In the centres of civilisation there was scarcely a faith of mankind which had not its votaries. It was an age of religious syncretism, of hospitality to diverse religious ideas, of the commingling of those ideas. These things facilitated the progress of Christianity. They made certain that if the Christian movement had in it the divine vitality which men claimed, it would one day conquer the world. Equally, they made certain that, as the very condition of this conquest, Christianity would be itself transformed. This it is which has happened in the evolution of Christianity from its very earliest stages and in all phases of its life. Of any given rite, opinion or institution, of the many which have passed for almost two millenniums unchallenged under the Christian name, men about us are now asking: But how much of it is Christian? In what measure have we to think of it as derived from some other source, and representing the accommodation and assimilation of Christianity to its environment in process of its work? What is Christianity? Not unnaturally the ancient Church looked with satisfaction upon the great change which passed over Christianity when Constantine suddenly made that which had been the faith of a despised and persecuted sect, the religion of the world. The Fathers can have thought thus only because their minds rested upon that which was outward and spectacular. Not unnaturally the metamorphosis in the inward nature of Christianity which had taken place a century and a quarter earlier was hidden from their eyes. In truth, by that earlier and subtler transformation Christianity had passed permanently beyond the stage in which it had been preponderantly a moral and spiritual enthusiasm, with its centre and authority in the person of Jesus. It became a system and an institution, with a canon of New Testament Scripture, a monarchical organisation and a rule of faith which was formulated in the Apostles' Creed.