For as much as I've written about the possibility of a distinct Christian political witness, I fear I have failed to underscore the profound and ultimate sense of competition between the contemporary polis and the witness of the Church.
Allow me, as I have so often done, to quote Oliver O'Donovan on this point:
In conclusion, it was possible for the apostolic church to look at the relation of church and secular government from one of two angles. On the one hand, government could be seen as thrust back by Christ's victory to the margins, there to be reauthorised to perform a single function of which the church outside the world stood in need for the time being. On the other hand, it could be seen as goaded by Christ's victory to a last desperate assertion of itself, momentarily overwhelming the church's solidarity in an alternative, massively smothering solidarity of refusal. Either way the victory of Christ was the key to the relation. The Messianic age was to be the age of ultimate choices and conflicts, in which the pluriform structures of political mediation would be propelled to a simple decision between two governments: the creative government of the Word of God and the predatory self-destructive government of human self-rule. In this age that decision must underlie all decisions.
Is there any wonder why the blood of the martyrs is the seed of the church? While human government is reauthorized, it is also destabilized and challenges us to make a fundamental decision between Caesar and Christ.