One of the worst misrepresentations of the Reformation teaching of God’s two kingdoms that I’ve heard goes like this: “Two kingdom theology means that we only have to live as Christians on Sunday but not the rest of the week.” This notion is completely mistaken in every way; it is absolutely not at all an implication of two kingdom theology. Here’s how David VanDrunen touches upon two kingdom theology and ethics in chapter seven of his book Living in God’s Two Kingdoms.
“…Christians have a responsibility to be involved in a broad range of cultural endeavors, that they can and should honor God by their righteous pursuit of such activities, and that they should perform these activities, as activities of the common kingdom under the Noahic [common grace] covenant, alongside of and in cooperation with unbelievers. Christians are Christians seven days a week, in whatever place or activity they find themselves, and thus they must always strive to live consistently with their profession of Christ.”
“Every Christian has the obligation to make morally responsible decisions about his cultural endeavors.”
“…Believers must strive to perform all of their cultural activities in a way consistent with their Christian identity, and this means, as a subject matter, that the Christian’s cultural activities should always be fundamentally different from unbelievers’. Christians are called not only to act in accord with God’s law at all times but also to do all things from faith (Rom. 14:23; Heb. 11:6) and all things for God’s glory (1 Cor. 10:31).” …Here then is one way in which cultural activity should be uniquely Christian: even in their most ordinary and mundane tasks, Christians must act from faith, in accord with God’s law, and for God’s glory. Whatever they do, they should ‘work heartily, as for the Lord and not for men’ (Col. 3:23).”
Of course, some advocates of two kingdom theology misunderstand the teaching and live ungodly, reckless lives. But someone who rightly understands the Reformation teaching of the two kingdoms will certainly not live like a Christian on Sunday and a pagan on Monday. Two kindgom theology not only includes the Reformation slogan soli Deo gloria, but also the third use of the law which says the Christian must obey God’s precepts to show him thanks for the salvation Christ won for us.
Finally, if you want to see how two kingdom theology works out in the realm of Christian bioethics, VanDrunen also wrote Bioethics and the Christian Life. The third chapter of this book, “Christian Virtues,” is an outstanding exposition of faith, hope, love, courage, contentment, and wisdom. I highly recommend both of these books. And again, to be clear, consistently Reformed two kingdom theology goes hand in hand with godliness, solid piety, obedience, and a life aimed at God’s glory.