The following is an excerpt from chapter four of J.I. Packer’s Knowing God.
The realization that images and pictures of God affect our thoughts of God points to a further realm in which the prohibition of the second commandment applies. Just as it forbids us to manufacture molten images of God, so it forbids us to dream up mental images of him. Imagining God in our heads can be just as real a breach of the second commandment as imagining him by the work of our hands.
How often do we hear this sort of thing: “I like to think of God as the great Architect (or Mathematician or Artist).” “I don’t think of God as a Judge; I like to think of him simply as a Father.” We know from experience how often remarks of this kind serve as the prelude to a denial of something that the Bible tells us about God. It needs to be said with the greatest possible emphasis that those who hold themselves free to think of God as they like are breaking the second commandment. At best, they can only think of God in the image of man–as an ideal man, perhaps, or a superman. But God is not any sort of man. We were made in his image, but we must not think of him as existing in ours. To think of God in such terms is to be ignorant of him, not to know him.
All speculative theology, which rests on the philosophical reasoning rather than biblical revelation, is at fault here. Paul tells us where this sort of theology ends: “The world by wisdom knew not God” (1 Cor 1:21 KJV). To follow the imagination of one’s heart in the realm of theology is the way to remain ignorant of God, and to become an idol-worshipper–the idol in this case being a false mental image of God, made by one’s own speculation and imagination.
In this light, the positive purpose of the second commandment becomes plain. Negatively, it is a warning against ways of worship and religious practice that lead us to dishonor God and to falsify his truth. Positively, it is a summons to us to recognize that God the Creator is transcendent, mysterious and inscrutable, beyond the range of any imagining or philosophical guesswork of which we are capable–and hence a summons to us to humble ourselves, to listen and learn of him, and to let him teach us what he is like and how we should think of him.
“For my thoughts are not your thoughts,” God tells us; “neither are your ways my ways,” for “as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts” (Is 55:8-9). Paul speaks in the same vein: “Oh, the depth of the riches of the wisdom and knowledge of God! How unsearchable his judgments, and his paths beyond tracing out! Who has known the mind of the Lord? (Rom 11:33-34).
God is not the sort of person that we are; his wisdom, his aims, his scale of values, his mode of procedure differ vastly from our own that we cannot possibly guess our way to them by intuition or infer them by analogy from our notion of ideal manhood. We cannot know him unless he speaks and tells us about himself.
But in fact he has spoken. He has spoken to and through his prophets and apostles, and he has spoken in the words and deeds of his own Son. Through this revelation, which is made available to us in holy Scripture, we may form a true notion of God; without it we never can. Thus it appears that the positive force of the second commandment is that it compels us to take our thoughts of God from his own holy Word, and from no other source whatsoever.