When fellow Christians speak of the separation of church and state I find it’s necessary to tease out what they mean by that.
Do they mean church should only be overseeing the personal dimensions of life while the state overseeing the political dimensions of life, as in a two kingdoms model? Or do they see separation in more counter cultural terms, and seek to exercise power differently to the powerful, as in a rival kingdoms model? In other words, is the state a type of Jerusalem that we should feel at home in or a type of Babylon that we should feel like exiles in?
Personally I lean towards the latter. The kingship of Jesus is not limited to one dimension of life. Jesus is Lord of all dimensions of life. Jesus is the king of kings, or president of presidents if you will. I see it this way: we are to be loyal to the state only to the extent that it doesn’t conflict with higher loyalties … and we can be assured that at some point those loyalties will come into conflict. At that point we will have to choose between two kings. We can’t follow both at the same time all the time.