From an excellent, brief article on Neo-Calvinism vs. Two Kingdoms theology by David Koyzis:
From my readings of Thomas Hobbes, John Locke, John Rawls and many other professed liberals, I have come to conclude that liberalism must be understood in terms of its longstanding quest to reduce the complexity of human communities to mere voluntary associations. This is the significance of the social contract, which is nothing less than a redefining of the proper task of the state. Rather than possessing a divine mandate to do justice (Psalm 82; Proverbs 29:4,14), political authority is now defined in terms of the collective wills of the individuals who ostensibly brought it into existence.
Two Kingdoms (2K) proponents don’t see it this way; they are more sanguine about the liberal order. Its undeniable success in keeping the peace proves it to be the fruit of the only principle that can guide us in the civil sphere: prudence.
This debate is very fruitful for Christian thought on our role in politics. It’s a little late to be having it, and I’m about to reveal my proclivities if I haven’t already—but now that perversion has joined murder as a right in American jurisprudence, it’s difficult to continue to imagine the liberal order to be benign. Because it is a voluntary association it is subject to the norms of the volunteers; if a majority move homosexual acts from the “immoral” category to the “moral”—and this has only just happened in America—then so it is and ever shall be (and we can’t even remember, conveniently, when we didn’t already think this way).
I can never get Fish out of my head on this point:
If you persuade liberalism that its dismissive marginalizing of religious discourse is a violation of its own chief principle, all you will gain is the right to sit down at liberalism’s table where before you were denied an invitation; but it will still be liberalism’s table that you are sitting at, and the etiquette of the conversation will still be hers. That is, someone will now turn and ask, “Well, what does religion have to say about this question?” And when, as often will be the case, religion’s answer is doctrinaire (what else could it be?), the moderator (a title deeply revealing) will nod politely and turn to someone who is presumed to be more reasonable. To put the matter baldly, a person of religious conviction should not want to enter the marketplace of ideas but to shut it down, at least insofar as it presumes to determine matters that he believes have been determined by God and faith. The religious person should not seek an accommodation with liberalism; he should seek to rout it from the field, to extirpate it, root and branch.
But this doesn’t and can’t mean that Christians expect the sword to advance the kingdom; it only means that while praying and hoping for and enjoying for peace (1 Tim. 2:2) we don’t give in to the status quo. Koyzis again:
The body of Christ is not undertaking to bring heaven to earth, but is merely seeking to fulfill the central command to love God and neighbour in all of life’s activities.
(And read one of the sets of posts I myself return to most frequently, the three “Levels of Bible Integration” we use at my employer to evaluate whether or not we are truly shaping a Christian worldview with our materials.)
(And read this essay I’ve found so helpful: “Not Ashamed! The Sufficiency of Scripture for Public Theology“)