Doug Wilson has been at the forefront of arguing for what he calls “Mere Christendom” of late, and I’m grateful to him for it. Even though we disagree on some important particulars, there’s nothing objectionable about this bit:
The mistake we made was this. If we want and need a “mere Christendom,” then we need to keep that Christendom from becoming sectarian. But when you pour a diluting agent into your theology willy nilly, unless you take care, the dilution will affect the essential aspects of the Christian faith, like the death and resurrection of Jesus, and not just the relative unimportance of the debate between supralapsarians and infralapsarians.
Mere Christendom needs to be thin when it comes to the differences between Lutherans and Methodists, Presbyterians and Baptists, and so on. But it needs to manage to do this without thinning out the contents of the Apostles Creed. It needs to be thick there.
This is largely why I can get along better with some Catholics than I can with some postmoderns. Even though the latter might affirm everything I say doctrinally, by revising the nature of propositions and their relationship to reality, they undercut the possibility of christendom (re)-covering the United States and reshape what we’re doing when we say the creed. Christendom was a possibility for the early church precisely because the creeds expressed truths that corresponded to reality in such a way that there were binding on all people, regardless of which language game they inhabited. As O’Donovan points out, the early church was sympathetic to one-world government precisely for this reason.
Which is to say, it’s hard to swallow some of the epistemological aspects of postmodernism and keep the mere Christendom around and running. Your nearest option is to head into the anabaptist notion of the church as a counter-polis, but then that tends to have a nasty gnostic streak that may make it untenable.
Better to sign up for mere orthodoxy of the classical variety and work to revive the mere Christendom that goes along with it.