Calvin, Harmony of the Law Part II, Intro on the Second Commandment; “No Images:”
Now we must remark, that there are two parts in the Commandment — the first forbids the erection of a graven image, or any likeness; the second prohibits the transferring of the worship which God claims for Himself alone, to any of these phantoms or delusive shows. Therefore, to devise any image of God, is in itself impious; because by this corruption His Majesty is adulterated, and He is figured to be other than He is. There is no need of refuting the foolish fancy of some, that all sculptures and pictures are here condemned by Moses, for he had no other object than to rescue God’s glory from all the imaginations which tend to corrupt it. And assuredly it is a most gross indecency to make God like a stock or a stone. Some expound the words, “Thou shalt not make to thyself a graven image, which thou mayest adore;” as if it were allowable to make a visible image of God, provided it be not adored; but the expositions which will follow [note: this is the intro to his exposition of the Second Commandment] will easily refute their error. Meanwhile, I do not deny that these things are to be taken connectedly, since superstitious worship is hardly ever separated from the preceding error; for as soon as any one has permitted himself to devise an image of God, he immediately falls into false worship. And surely whosoever reverently and soberly feels and thinks about God Himself, is far from this absurdity; nor does any desire or presumption to metamorphose God ever creep in, except when coarse and carnal imaginations occupy our minds. Hence it comes to pass, that those, who frame for themselves gods of corruptible materials, superstitiously adore the work of their own hands. I will then readily allow these two things, which are inseparable, to be joined together; only let us recollect that God is insulted, not only when His worship is transferred to idols, but when we try to represent Him by any outward similitude.
Source: http://www.puritanboard.com/f18/reformed-iconoclasm-83016/, Comment #3