Everyone already knows, I suppose, that the radical, supposedly Lutheran, view of the two kingdoms (R2kT for short) advocated by folks like Darryl Hart is contrary to the 1646 (original edition) Westminster Confession of Faith (WCF1646). In fact, advocates of R2kT typically brag that the American revisions to the Westminster Confession (WCF-AR) removed the language that they would have to take an exception to (as well as other language, which appears to be unrelated).
What is less well-known is that the Article 36 of the 1618 (original edition) Belgic Confession (BC1618, one of the three forms of unity) says the same thing. Remarkably, it is Darryl Hart who is now pointing out this fact (link to his post).
Hart has been fond of mislabeling traditional Reformed believers (folks who subscribe to the BC1618 or WCF1646) as Kuyperians. Now, he expresses shock that "Kuyperians" don't listen to Kuyper - after all, Kuyper himself took an exception to Article 36.
Interestingly, Kuyper was somewhat more frank than the R2KT proponents on this matter, for he stated: "We do not at all hide the fact that we disagree with Calvin, our Confessions, and our Reformed theologians." Whereas it seems that some folks who disagree with Calvin, the Confessions, and the Reformed theologians want to insist that they are "Reformed" while their "Reformed Baptist" brethren are not.
What is interesting is that, despite his exception to Article 36, Kuyper is not radical enough for Hart. After all Kuyper "apparently launched" "transformationalism" - by which Hart apparently means the notion (be prepared to be shocked) that the gospel may transform not only individual people but whole societies of people.
Postscript: Of course, Hart is now bragging about how American revisions to the Belgic Confession axed the corresponding parts regarding the duties of the civil magistrate. Those Americans - what can I say!
The English also revised (though not as radically) Article 37, which originally was consistent with the other Reformed confessions, and which could still be read consistent with them, though it seems unlikely that such was the intent of the revisers.
However, at least to my knowledge, there is no American or Anglican revisions of the Scottish Confession of Faith (1560), which declares essentially the same thing as the other Reformed confessions with respect to the Civil Magistrate, at chapter 24. The Scottish Confession was superceded, in the Church of Scotland, by the original Westminster Confession of Faith.