The Christian doctrine of God, in Athanasian days, triumphed where Greek philosophy failed. It accepted the challenge of Greek thought, it recognised the demands of the speculative reason, and found in itself the answer which, before the collision with Hellenism, it unconsciously possessed. It is challenged again by the metaphysics of our day. We may be wrong to speculate at all on the nature of God, but it is not less true now than in the first centuries of Christianity, that, for those who do speculate, a Unitarian, or Arian, or Sabellian theory is as impossible as polytheism. If God is to be Personal, as religion requires, metaphysics demands still a distinction in the Unity which unitarianism is compelled to deny. But, further, the Christian doctrine of God is challenged by the science of nature. Science, imperiously and with increasing confidence, demands a unity in nature which shall be not external but immanent, giving rationality and coherence to all that is, and justifying the belief in the universal reign of law. But this immanence of God in nature unitarian theism cannot give, save at the price of losing itself in pantheism. Deistic it might be, as it was in the last century; deistic it can be no longer, unless it defiantly rejects the truth which science is giving us, and the claims which the scientific reason makes. It remains then for Christianity to claim the new truth and meet the new demands by a fearless reassertion of its doctrine of God. It has to bring forth out of its treasury things new and old,--the old almost forgotten truth of the immanence of the Word, the belief in God as 'creation's secret force,' illuminated and confirmed as that is by the advance of science, till it comes to us with all the power of a new discovery. Slowly and under the shock of controversy Christianity is recovering its buried truths, and realizing the greatness of its rational heritage. It teaches still that God is the eternally existent One, the Being on Whom we depend, and in Whom we live, the source of all reality and the goal to which creation moves, the Object alike of religion and philosophy, the eternal Energy of the natural world, and the immanent reason of the universe. It teaches that He is the eternally Righteous One, and therefore the Judge of all, irrevocably on the side of right, leading the world by a progressive preparation for the revelation of Himself as Infinite Love in the Incarnation of the Word, stimulating those desires which He alone can satisfy, the yearning of the heart for love, of the moral nature for righteousness, of the speculative reason for truth. When men had wearied themselves in the search for a remedy for that which separates men from God, the revelation is given of Him Who 'shall save His people from their sins.' And when reason had wandered long, seeking for that which should be Real and yet One, a God Who should satisfy alike the demands of religion and reason, the doctrine of the Trinity is unfolded. It