Christians, like most other theists, differentiate between worshipping an acutal god and worshipping a hunk of wood, stone, artwork, etc. Christians, in general, say they believe they are actually worshipping the invisible wizard king of the universe.
But if you look at Christianity, it comes down to 2 basic concepts:
1. The Bible is magically true. At least some of it.
2. Jesus is magically god. At least some times.
Let's take #1 first. Christians are stuck with the Bible since it is the most well-known and accepted book about Jesus. In many evangelical Christian churches, the members all carry Bibles to every service, even though the preacher is there to read it for them. And even the non-fundamental, so-called liberal theologians will cite many Bible passages they love. The same theologians will admit that god is vastly cosmic and most unknowable to humans. I submit to you that if god is unknowable and invisible, but you are carrying a magic book around and quoting from if for magic wisdom, in reality, you are worshipping the book, and not the invisible untouchable god.
Now for #2: Christians all say they love Jesus and that Jesus is somehow magic. Christians say they pray to Jesus. Well, how do Christians know what Jesus looks like? The answer is that they imagine Jesus based on the pictures they were shown of Jesus when they were children. And since there were no photographs of Jesus taken while alive, and there are no known portraits created in his lifetime, all pictures of Jesus are fanciful. Christians who visualize Jesus when they pray are really praying to a created idol based on imaginary images.
Now, a Christian might say he is not imagining a visual Jesus when he prays, but that he is instead conjuring up a concept of Jesus based on his reading of the Gospels. Well, even if this dubious claim is so, then the Christian is actually worshipping his magic book again...so that is idol worship either way.
The point is, the charactheristics modern humans attribute to Biblegod, universiality, invisibility, perfection, etc. make Biblegod impossible for humans to mentally hold in their head. Consequently, they will worship symbols instead, magic crosses they put around their necks, magic books, magic statures, etc.
It's all idoloatry, just like the other religions.