Very few American travelers to certain African countries come down with yellow fever. So, it may seem unjust to require American travellers to get a yellow fever vaccination before entering those countries. On the other hand, the reason for the low incidence of yellow fever may be precisely because American travelers are required to get vaccinated against yellow fever before entering.
The point of the analogy is that sometimes a given state of affairs has an underlying cause. Ignoring that underlying cause can lead to drawing wrong conclusions from the state of affairs.
Van Drunen and similar folks make this error when they make the "Argument From Cultural Homogeneity" (see the pdf linked). But there is a significant objection to this argument. Mattson explains:
Look at it again: (A) "There is nothing distinctively 'Christian" about cultural pursuits because (B) there is widespread cultural homogeneity." But what if I argue the other way around: (B) there is widespread homogeneity precisely because (A) Christians have historically been effective in transforming cultural norms and expectations? This is precisely the conclusion VanDrunen does not want readers to draw. So it is not enough for him to simply point to the fact of cultural homogeneity. He has to account for it.The way that VanDrunen attempts to account for this homogeneity is by reference to God's covenant with Noah. Mattson skillfully rebuts this point:
Think about it for a moment. What is the covenant with Noah all about? At its core, it is about stability and regularity. Never again will God destroy all living creatures with a flood. God promises that "as long as the earth endures, seedtime and harvest, cold and heat, summer and winter, day and night will never cease" (Gen. 8:22). The refrain, "never again" is repeated three times (8:21; 9:11, 15). The sign of the rainbow will be an enduring sign of an "everlasting covenant" between God and all living creatures. In other words, the commitments God makes in this covenant are inalterable. God's promises simply cannot fail. God commits to never destroy the earth by a flood? Sure enough, he has made good on this promise. God commits to uphold the regularity and uniformity of nature? Sure enough, God has made good on this promise. The sun still rises and winter still follows autumn. Now let us ask: what if God promised that there will be widespread homogeneity of cultural norms and expectations among the human race? Given God's nature and the nature of the Noahic covenant, then there has been, in fact, widespread cultural homogeneity since the time of Noah!There's plenty more in the pdf linked above. It does remind me a little of Frame's comment in "The Escondido Theology": "Indeed, God's covenant with Noah is religious through and through, even on the narrowest definitions of "religion." ... God's covenant with Noah is an administration of God's redemptive grace, religious through and through, just as those with Abraham, Moses, David, and Christ." (p. 137) This stands in contrast to VanDrunen's assertion (quoted by by Frame on p. 136):
Few suggestions can be more historically ignorant and empirically false. To state the blindingly obvious: the history of the human race is not a history of cultural homogeneity.
Furthermore, Genesis 9 makes it evident that the covenant of common grace regulates temporal, cultural affairs rather than more narrowly religious affairs pertaining to salvation from sin. (pp. 27-28)(as quoted by Frame)
One of the problems of VanDrunen's view on the two kingdoms is that it suffers from the same kind of ontological problem as atheistic morality. Atheists refuse to acknowledge that their standards of morality are borrowed property. The VanDrunen-style two kingdoms view makes the same kind of mistake, to a lesser degree, in terms of committing the cultural amnesia Mattson describes.