_God is the first principle, the unconditioned cause of all existence._ This is the answer of Christian doctrine to the great problem presented for solution in the preceding chapter. Whether this fundamental presupposition shall be finally accepted as the only adequate solution of the problem of existence will depend in a large degree upon our apprehension of the Christian idea of God. We shall, therefore, open the discussion by asking the question--What is the content of our conception of God? Dogmatic theology might rest satisfied with the simple affirmation, "_God is_ GOD,"[17] as against all the captious demands of science, were it not necessary to render an account to itself of what, at first sight, might be pronounced a "sublime tautology." For, while it is hereby confessed that God in his essential being is incomprehensible and ineffable, so that to the Christian as well as to the philosopher he is "the great Unknown," still it is not hereby admitted that it is absolutely impossible to know God. To affirm that God is absolutely "the Unknowable" is simply to assert his unreality. Mr. Martineau has finely observed that this term is self-contradictory; for we affirm by the use of it that we know so much that He can not be known. Nay, it assumes the existence of God, and in the same breath separates us from Him forever. But if it be admitted that God _is_, it can not be absolutely impossible to know _what_ He is. The knowledge of existence and the form of existence mutually condition each other. There must be something in the understanding answering to the term in the language of mankind, and there must be something in the realm of being which is the ground of the idea in the reason of Man. The heathen have a presentiment, a dim intuition of the "unknown God," and the inspired teacher may so "declare Him" in human language that his hearers may receive a definite notion, and attain to a practical knowledge of God.