Christianity, with over 2 billion adherents, is the largest religion in the world. It is also the fastest growing. Thanks mostly to Africa and Asia, there 25 million believers added each year. Yet in academic circles, religion is often relegated to the background or worse, ignored as myth and fairytale. Religion's importance is hard to ignore, but its role in a diverse democracy is even harder to understand.
For centuries Europe, one of the few places Christianity is shrinking, has decided to combine church and state, with devastating results (Crusades, Spanish Inquisition, etc). But even today, the strong ties of European governments and their preferred religion have hurt both church and state. The British government, although it gives no direct funds to the Church of England, is much closer than most Americans would be comfortable with. For example, the Church of England gets 26 unelected members in the House of Lords (like our Senate). More recently, the United Kingdom's Big Society plan, though appealing in some ways, could tie the two financially even tighter.
Religious freedom, perhaps one of the United States' greatest exports, has allowed for a flourishing religious and secular society. Political institutions should not hinder or support Christianity (or any religion), because Christians have different perspectives on politics. So what is the role of the church in the state? In a lecture to to U.C. Berkley, Pastor Tim Keller (earlier) describes the role of the church as one that "shows us what human flourishing looks like", then we let the political debate begin.