Michael Horton has an irenic blog post on the Two Kingdoms debate, in which he complains about what he believes are mischaracterizations of the view. He writes that he can only speak for himself, but additionally recommends David VanDrunen's Living in God's Two Kingdoms.
The trouble is, Horton's articulation of 2KT is a far cry from the presentation found in VanDrunen's book. I suggest that Mike actually read the book he is recommending. Horton wants to bring the "two" kingdoms into some kind of existential unity. He is zealous to maintain that the 2KT paradigm does not imply that there is nothing distinctively "Christian" about cultural engagement. Yet VanDrunen emphasizes, repeatedly, exactly that claim.
"A two-kingdoms doctrine, distinguishes what is uniquely 'Christian' from what is simply 'human' [....] Generally speaking, to be 'human' here and now means living in the common kingdom under the Noahic covenant. Christians share the life and activities of the common kingdom with all human beings. What differentiates them from the rest of humanity is their identification with the redemptive kingdom and all that that entails." (p.167)
"Learning, working, and voting are not uniquely Christian tasks, but common tasks. Christians should always be distinguished from unbelievers subjectively: they do all things by faith in Christ and for his glory. But as an objective matter, the standards of morality and excellence in the common kingdom are ordinarily the same for believers and unbelievers: they share these standards in common under God's authority in the covenant with Noah." (p.31)
"[T]he normative standards for cultural activities are, in general, not distinctively Christian. By this I mean that the moral requirements that we expect of Christians in cultural work are ordinarily the same moral requirements that we expect of non-Christians, and the standards of excellence for such work are the same for believers and unbelievers." (p.168)
"[A] writer promotes a 'contemporary Christian perspective on business,' which promotes the principles of fair trading practices for workers, healthy local businesses, and Christian-run start-up businesses that 'lovingly serve the needs of fellow citizens.' [These] principles are admirable, but there is nothing distinctively 'new creation' or 'Christian' about [...] them. All of these principles are grounded in the present created order and the terms of the Noahic covenant." (p.193-4)
Horton is trying to join together what VanDrunen has sundered. Referring to Calvin and Luther, Horton writes: "[The Two Kingdoms] are not two tracks that never touch; they are two callings that intersect." Yet the entire burden of VanDrunen's book is to deny that the two kingdoms ever actually intersect. Yes, people inhabit them at the same time, but the realms themselves do not overlap or commingle. Page after page urges Christians to never confuse or commingle these two realms. This is not even to mention the strict identification in the book of the redemptive kingdom with the institutional church (again, something VanDrunen articulates emphatically). This precludes him from making Horton's crypto-Kuyperian move distinguishing between the church as organization and organism.
All of this is to say: Michael Horton needs to stop being "baffled" at these characterizations of the Two Kingdoms paradigm. They are taught explicitly and emphatically in the very book he is recommending. Having spent a good deal of time carefully reading VanDrunen's book, Tim Keller's generalizations (the immediate source of Horton's ire) strike me as perfectly reasonable and fair.
In my carefully considered opinion, David VanDrunen argues for an almost complete dualistic split between heavenly and earthly callings. If Horton wants to put Humpty Dumpty back together again and view them as unified and complimentary, I suggest he walk down the hall and have a nice, long visit with his colleague. Because from the looks of Horton's blog post, the right hand at WSCAL doesn't know what the left hand is doing.