From the definition of Theology as the science concerning God follows the necessity of its being based on revelation. In scientifically dealing with impersonal objects we ourselves take the first step; they are passive, we are active; we handle them, examine them, experiment with them. But in regard to a spiritual, personal being this is different. Only in so far as such a being chooses to open up itself can we come to know it. All spiritual life is by its very nature a hidden life, a life shut up in itself. Such a life we can know only through revelation. If this be true as between man and man, how much more must if be so as between God and man. The principle involved has been strikingly formulated by Paul: ‘For who among men knoweth the things of a man, save the spirit of the man which is in him? even so the things of God none knoweth, save the Spirit of God’ [1 Cor. 2.11]. The inward hidden content of God’s mind can become the possession of man only through a voluntary disclosure on God’s part. God must come to us before we can go to Him. But God is not a personal spiritual being in general. He is a Being infinitely exalted above our highest conception. Suppose it were possible for one human spirit to penetrate directly into another human spirit: it would still be impossible for the spirit of man to penetrate into the Spirit of God. This emphasizes the necessity of God’s opening up to us the mystery of His nature before we can acquire any knowledge concerning Him. Indeed, we can go one step farther still. In all scientific study we exist alongside of the objects which we investigate. But in Theology the relation is reversed. Originally God alone existed. He was known to Himself alone, and had first to call into being a creature before any extraneous knowledge with regard to Him became possible. Creation therefore was the first step in the production of extra-divine knowledge.
Biblical Theology: Old and New Testaments (Edinburgh, Scotland; Banner of Truth, 1975), p. 3-4.