Theology is word work. It is a linguistic enterprise, which means it is a cultural enterprise. For that reason, I sometimes think that biblical theology fails - not at being biblical, but at being theology. Take the term "kingdom of God". Biblically/historically speaking, this was term was at the centre of Jesus's proclamation. As 1st Century Palestinian theology, its articulation would have resonated with the culture of its day. Of course this isn't incidental, because it was necessary for Jesus to be a product of this particular culture at this particular time if he was to be the rescuer of the world.
My issue is that the term "kingdom of God" carries little cultural weight in the time and place I was raised in. In the 1st Century, to confess Jesus as king was, as others have noted, to simultaneously confess that Caesar was not. This kind of confession was political, subversive, and inherently relevant, because it was rooted in the language and practices of its time. An Irishman saying that "Jesus is king" no longer has that same direct impact. I do not speak of kings, I do knot know what it is to have a king. The confession Jesus is King means almost as little to me as the confession Jesus is Sultan. Neither metaphor is rooted in the culture I have grown up in, therefore neither metaphor provides me with the kind of theology that is needed today.
I have, as usual, no prescriptions. In fact I think my diagnosis needs a heck of a lot more work. I'm going on instincts here, and little else. I think the broader point I'm trying to make is that what is biblical is not necessarily theological. Or to put it another way, what is faithful to the Bible is not necessarily faithful to the God of the Bible today.