The second commandment is by far the most important scriptural passage dealing with worship.
4 Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth.
5 Thou shalt not bow down thyself to them, nor serve them: for I theLord thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me;
6 And shewing mercy unto thousands of them that love me, and keep my commandments.
When the Lord condemns one particular sin in the Ten Commandments, He is implicitly condemning all related sins and commanding the corresponding virtues (WLC 99). So, for example, the ninth commandment, which forbids bearing false witness, implicitly forbids us from doing anything that "is prejudicial to truth, or injurious to our own or our neighbour's good name" (WSC 78). It also requires the "maintaining of and promoting of truth between man and man, and of our own and our neighbor's good name" (WSC 77). When we read that God condemns idolatry in the second commandment, we have to ask ourselves what idolatry represents. Idolatry is simply one of the most egregious examples of unacceptable worship. The making of images for use in worship is the very epitome of what Paul calls "will-worship" (Col 2:22-23). It is the archetype of all man's attempts to worship God through the work of his hands. So in the second commandment, God forbids not only the making and worshiping of images, but any form of worship fashioned by the hands of men rather than by God. This is clear from the example God gives just a few verses later to make His intent clear and to show us how to interpret the second commandment. He says, "And if you make an altar of stone for Me, you shall not build it of cut stones, for if you wiled your tool on it, you will profane it" (Ex 20:25). God was teaching the Israelites by example that all their own efforts at improving on what God has commanded are in fact no different from the grosser forms of idolatry. All attempts at adorning the worship in order to make it more appealing to the human senses, whether carving an image outright or simply improving upon an altar, were forbidden.
The connection between the second commandment and the RPW becomes even clearer when we reflect on the nature of the idolatry it forbids. An idol is not just a representation of another god, thought it can be that. The grossest forms of idolatry in Scripture are those in which men have tried to worship the true God in a manner in which He has not commanded. When the Israelites at Sinai created a golden calf to worship, they did not understand it to be a new god, a replacement for the Lord. They proclaimed it to be the God who had delivered them from Egypt. Aaron built an altar before it and proclaimed a feast to the Lord (Ex 32:4-5). What made the golden calf idolatrous was not that it was a new god, but that it was an attempt to worship the true God in a manner of their own devising.
The root problem is not the carving of a tangible token of the presence of God, but the fashioning of such a token without the express command of God. God did, after all, command the construction of a rather elaborate physical focal point for His worship, the tabernacle and later the temple, and the design included carved cherubim above a golden ark. But HE reserved the right to determine what was appropriate and what was not. Any carving was to be done at His direction, not at the whim of the worshiper.
The question of what constitutes an idol is a difficult one, but the example forbidding carved altars tells us most of what we need to know. A carved altar was an attempt to make the worship of God more pleasing to the senses. The point of this restriction was to teach the Israelites to keep their hands to themselves in matters of worship. Novelty, artistic license and innovation were forbidden, no matter how reasonable or innocuous the additions might appear to the worshiper.
Christ is the perfect realization of the need we feel for God to be present physically and to be manifested in a manner discernible to the human senses. This is a legitimate need. That is why, in the absence of Christ in bodily form, God has given us what Reformed theologians have called "the visible word" in the form of the sacraments. The point of the second commandment is that, though God understands the need for a tangible, even visible, token of His presence in worship, He is the only one who can provide it.
(Songs of Zion, p. 163-165)
(Songs of Zion, p. 163-165)