God really is what we believe Him to be, so far as our idea of Him is determined by the revelation which He has made of Himself in his works, in the constitution of our nature, in his word, and in the person of his Son. To know is simply to have such apprehensions of an object as conform to what that object really is. We know what the word Spirit means. We know what the words infinite, eternal, and immutable, mean. And, therefore, the sublime proposition, pregnant with more truth than was ever compressed in any other sentence, “God is a Spirit, infinite, eternal, and immutable,” conveys to the mind as distinct an idea, and as true (i. e., trustworthy) knowledge, as the proposition “The human soul is a finite spirit.” In this sense God is an object of knowledge. He is not the unknown God, because He is infinite. Knowledge in Him does not cease to be knowledge because it is omniscience; power does not cease to be power because it is omnipotence; any more than space ceases to be space because it is infinite.

Charles Hodge, Systematic Theology, Vol. 1, 339.