Q: What does the second commandment forbid?
A: The second commandment forbids our worshiping God with images or in any other way not established in His word.
Protestants have taken Roman Catholics to task with this commandment, arguing that statues of the saints and the Virgin Mary count as idols, and Muslims have, likewise, argued that Christians constantly make images of God and the Son of God, while their religion strictly forbids such heresy. Again, though, I think a proper reading of this commandment goes much deeper, for it forbids distorting our understanding of Him, especially and specifically truncating who He is through limiting frameworks or metaphors.
And yet, again, we constantly do this; we cannot help but doing this. We understand God through what we know; our very capacity for abstraction essentially works through metaphors. We think of God as a tyrant, a father, a clockmaker, an artist, a shepherd, a lion, a friend, and so on, and so on. None of these can really encapsulate all that God is, and it is only through the redemptive grace of our salvation can we hope to obey.
That said, some paradigms are truer than others, are even endorsed in Scripture, and we need to be rigorous about how our conceptions and preconceptions conform to what we find revealed in the Word. We need to beware, for example, of adopting a kind of prosperity gospel and thinking of God as Santa Claus or a karmic vending machine. Or live in constant self-flagellation because we only see Him as a stern judge or a demanding parent. Or abuse our freedom because we think of Jesus as the ultimate hippie. We need to be sure that when we worship, we worship the right God — and that as we worship, we open ourselves up to an encounter with Him that will challenge our trapped minds.
Moreover, this commandment invites us to listen to our children intently and take seriously what they say. They will tell us how they understand God, and we need to be on hand to enrich and correct that understanding. Alas, their understanding of God will inevitably be informed by our own example as the primary authority in their lives. We are His ambassadors to our families and to the world, His chosen shadows; we must take care in how we are shaped.