The point here is not just that an image represents God as having a body and parts, whereas in reality he has neither. If this were the only ground of objection to images, representations of Christ would be blameless. But the point really goes much deeper. The heart of the objection to pictures and images is that they inevitably conceal most, if not all, of the truth about the personal nature and character of the divine Being whom they represent.
To illustrate: Aaron made a golden calf (that is, a bull-image). It was meant as a visible symbol of Jehovah, the mighty God who had brought Israel out of Egypt. No doubt the image was thought to honor him, as being a fitting symbol of his great strength. But it is not hard to see that such a symbol in fact insults him, for what idea of his moral character, his righteousness, goodness and patience could one gather from looking at a statue of him as a bull? Thus Aaron's image hid Jehovah's glory.
In a similar way, the pathos of the crucifix obscures the glory of Christ, for it hides the fact of his deity, his victory on the cross, and his present kingdom. It displays his human weakness, but it conceals his divine strength; it depicts the reality of his pain, but keeps out of our sight the reality of his joy and his power. In both these cases, the symbol is unworthy of most of all because of what it fails to display. And so are all other visible representations of deity.
Whatever we may think of religious art from a cultural standpoint, we should not look to pictures of God to show us his glory and move us to worship; for his glory is precisely what such pictures can never show us. And this is why God added to the second commandment a reference to himself as "jealous" to avenge himself on those who disobey him: for God's "jealousy" in the Bible is his zeal to maintain his own glory, which is jeopardized when images are used in worship.
In Isaiah 40:18, after vividly declaring God's immeasurable greatness, the Scripture asks us: "To whom, then, will you compare God? What image will you compare to him?" The question does not expect an answer, only a chastened silence. Its purpose is to remind us that it is as absurd as it is impious to think that an image modeled, as images must be, upon some creature could be an acceptable likeness of the Creator.