One of the key points of contention between Free Churches and all other Christian communions lies in their posture towards what is commonly (and crudely) called “Constantinianism”. While figuring out the precise definition of what constitutes Constantinianism has filled entire books, at the simplest level we can say that Constantinianism constituted at least a certain sensibility about the logic of Christian participation and investment in political affairs of the Roman Empire (or the Byzantine Empire, or the Holy Roman empire, or the Frankish princedoms, or whatever). After Constantine it was more or less assumed that the church was part of (perhaps the definitive part of) the social structure of the world and had certain responsibilities and privileges that derived from that status. The overarching point is that churches which accept the basic structure of Constantinianism assume that the church is in some sense the “spiritual” and “religious” chaplain of the social order. It is the religious part of the social and political fabric of the nation in question which supports the powers that be through attending the spiritual needs of the people and providing a conscience to the wider society.
Now, to be sure I don’t want to paint too monolithic a picture of the post-Constantinian church. There were a great many Christians, both within monastic and lay movements, and within the church hierarchy throughout the centuries which stood against the idolatrous use of power and violence. However, there were also a great many forms of complicity with such forms of power. While Jesus insisted that his followers are to be servants to one another in contrast to the Gentiles who lord it over one another, the post-Constantinian church was often unable to embody the kind of kenotic, self-dispossessing leadership that Christ mandated. Political power in the world just doesn’t lend itself to one who would empty himself and the church, willy-nilly ended up often transposing the cruciform power of Christ with the triumphalist power of the crusader’s sword or the inquisitor’s rack.
Of course, in many respects Constantinianism is a thing of the past. Churches no longer have the same level or sort of power to shape political affairs in the world as they once did. However, the basic structure of Constantinianism does remain in most churches. Not simply through a sort of folk relgion that conflates Christianity and patriotism (as annoying as that is), but through a basic assumption that the church is to serve as a sort of “leaven” in society, stabilizing it, making it more moral, more just, more generally habitable. Although much of the church’s immediate power is gone, there is a general social conservatism that remains among most churches today. They, more or less, view their duty to the world (at least in the West), as one of helping to preserve and transform social life in the wider society.
The Free Churches, by contrast have stressed that the church is itself a society that is, in a very real sense incommunicable to the unbelieving world. The kind of transformed social relations that are inherent to the gospel message cannot be “communicated” to those who reject the gospel message in anything other than an invitational sense. The church has, according the Free Church vision, no mode of social transformation to offer the world than conversion, baptism, and repentance. As such the church cannot become the chaplain of the social order (even the occasionally-dissenting chaplain). The church, on the Free Church self-understanding has a supra-national unity which qualifies and controls all other allegiances and loyalties. As such, the Free Churches have rejected the use of violence in defense of justice. Since the unity of the church supersedes all other loyalties, Christians cannot allow foreign political powers to order them to kill one another without making a mockery of the Eucharist and the call to discipleship. Likewise, since the church’s missional mandate involves all creation, Christians cannot make war on unbelievers as their mission in the world is to bring the gospel to everyone.
The point of all of this is that the ecumenical vision of the Free Churches is profoundly shaped by the rejection of the Constantinian synthesis. If Christians are not free to wield any power other than the power of the cross, and if there is no worldly political formation which can truly claim the allegiance of Christians, then what would “full, visible Christian communion” look like? The Free Churches are not interested in a merely structural union or federation of churches which does not repudiate the Constantinian settlement. “The nature of the unity we seek” is a supra-national political unity which stands against all other loyalties, directly in competition with the claims of our contemporary Empires and Caesars. Within the “Free Church ecumenical style” (Yoder), there is no room for movements towards reunion that do not take the radically particular character of Christian ethics with the utmost seriousness. Whatever unity we seek, it will come at the cost of death and resurrection for all if it is the unity of the gospel. And that unity cannot be based on a common denominator or a structural integration. It must be based on the all-embracing call of Christ to a life of non-coercive, kenotic, cruciform discipleship into which all are welcomed as brother and sisters.