"Do not make idols"
(For pt.1 see here)
Not only had Israel broken the first law. Judah had done this too, and had not been exiled yet. The ultimate reason Israel was exiled, and the reason each and every King of Israel was condemned by God was the “Sin of Jeroboam.” Ultimately it boiled down to a transgression of the second law.
When Jeroboam became the first King of the northern kingdom, he knew that he could not let his people go to Jerusalem to worship. Their loyalties would be divided. So he set up a rival worship of Yahweh in Bethel and Dan. He constructed two golden bulls, and told the people that they were Yahweh and commanded them to gather at one of the two places to worship God.
This was such a great sin, that all other kings of Israel were judged by whether they followed his practice or not. The nation had always mixed the worship of God with paganism, and this was evil in the sight of God. But ultimately what did Israel in was the “sin or way of Jeroboam.” This was the empty worship of the true God. A false religion set up around a true God. This sin was held against every following King of Israel; even the few considered “good” kings held to this sin.
So what we really have here in II Kings 17 is the story of a false religion centered on a true God; it matters not if an idol represents the true God, it is still an idol! The second commandment is all about forbidding religion, not a repeat of the first commandment. Many people are confused by the first and second commandments. The first says, “Have no other gods.” The second says, “Make no idols.” If you don’t have any gods, why would you make idols? The answer is, of course, that God does allow one God to be worshiped: Him. So the second commandment could be read, “In worshiping Me, make no idols or representations as the pagans do.” God did not call the nation of Israel to Him to make yet another religion. Mankind had been making religions since the fall. God called them to a covenant, a relationship. Jeroboam’s great sin was that he turned God into simply another local deity, and made a whole new religion to worship him.
The second commandment is broken when we worship God but make Him in our own image, our own liking. Whenever we cease to have a growing relationship with the living God and instead fashion a representation of what we know Him to be and never see Him anew. Whenever we cease to seek Him out and simply become comfortable in the religious customs (or traditions) we have made.