I pulled this quote of Karl Barth from Hans Urs von Balthasar's article on A Divided Church (see below). Barth's comments stand on their own as a classic appraisal of our current divisions, and so are worthy of our consideration.
The plurality of churches ... should not be interpreted as something willed by God, as a normal unfolding of the wealth of grace given to mankind in Jesus Christ [nor as] a necessary trait of the visible, empirical Church, in contrast to the invisible, ideal, essential Church. Such a distinction is entirely foreign to the New Testament because, in this regard also, the Church of Jesus Christ is one. She is invisible in terms of the grace of the Word of God and of the Holy Spirit, . . . but visible in signs in the multitude of those who profess their adherence to her; she is visible as a community and in her community ministry, visible in her service of the word and sacrament.... It is impossible to escape from the visible Church to the invisible.
If ecumenical endeavor is pursued along the lines of such a distinction, however fine the words may sound, it is philosophy of history and philosophy of society. it is not theology. People who do this are producing their own ideas in order to get rid of the question of the Church's unity, instead of facing the question posed by Christ.... If we listen to Christ, . we do not exist above the differences that divide the Church: we exist in them.... In fact, we should not attempt to explain the plurality of churches at all. We should treat it as we treat our sins and those of others.... We should understand the plurality as a mark of our guilt (K. Barth, Die Kirche und die Kirchen. Theol., 9- 10).