Karl Barth’s slim book, The Church and the Churches, is a little nugget of theology. What’s more it’s a nice show piece of Barth’s theological method. Take this lovely passage on the nature of the quest for Christian unity (pp 18-20):
The quest for the unity of the Church must in fact be identical with the quest for Jesus Christ as the concrete Head and Lord of the Church. The blessing of unity cannot be separated from Him who blesses, for in Him it has its source and reality, through his Word and Spirit it is revealed to us, and only in faith in Him can it become a reality among us. I repeat: Jesus Christ as the one Mediator between God and man is the oneness of the Church, is that unity within which there may be a multiplicity of communities, of gifts, of persons within one Church, while through it a multiplicity of churches are excluded. When we confess and assert that it belongs to the Church’s commission to be one Church, we must not have in mind the idea of unity, whatever its goodness and moral beauty may be — we must have Him in our mind; for in Him and in Him only do those multiplicities within the Church possess their life, their scope, their dignity, rightfulness and promise…
Consequently Barth calls a spade a spade, insisting that divisive multiplicity between churches is nothing less than sin. And yet, he can also acknowledge that we seem backed into a corner here, since division often results from our faithfulness to the Lord Jesus Christ (pp 31-32):
It is unthinkable that whichever way one looks and listens, one should hear people saying, in quiet or vehement tones, with kindly under-statement or undisguised sternness, “You have a different Spirit from ours.” Yet that is just what actually results from the multiplicity of the churches; to wash our hands of it, or to prescribe doses of love, patience and tolerance as a cure, is futile. Such prescriptions may serve our turn almost anywhere else, but it is hopeless to mediate between churches by such methods — unless the churches are dead already. If they are alive, and if we are listening to Christ’s voice, then it is not a matter of opinion but of faith that over against the doctrine, order and life of other churches we should utter a more or less emphatic No at certain decision points, that we should draw the line and thus be compelled to endorse the multiplicity of the churches.
Hence the paradox.