The Christian churches today are in a deplorable state of division. One of the things that hinders the resolution of these divisions, or lessens the motivations of those in the church to work diligently for the sort of reform that would lead to their elimination if followed through, is a sense of complacency held by many in Reformed churches today. Many people will confess that there are divisions, and that we ought to work for their elimination, but they are lulled into thinking the situation better than it is by the feeling that we don't really need to have organic union among all the churches of Christ. Just as congregationalists/independents lull themselves into security regarding the disunity of the church (and thus split into thousands of mini-denominations) by their erroneous doctrine that church power does not extent beyond the local congregation (so that they hold that gatherings beyond the congregational level have only advisory and not binding authority), so many Presbyterian/Reformed people today have been lulled into security by the sense that the organic unity of the church need only extend up to a certain level, and after that we can adopt the model of the independents.
There is generally a recognition that congregations are under regional assemblies (presbyteries), and that presbyteries are under larger assemblies (often called general assemblies or synods), but at this point in the minds of many, things seem to begin to break down. There is a failure to be as concerned as we ought to be that within a single nation, there are multiple Reformed denominations with different general assemblies, and that congregations of these different denominations often co-exist in the same areas. There is often a degree of concern expressed regarding this situation, but it seems not to be as urgent in the minds of many as it ought to be; and this is partly owing, I think, to the existence of non-binding organizations and confederacies (like NAPARC in North America) which give to the churches a sense that they are getting along and cooperating, even though they are not in full, organic communion with one another under one general council.
Things are even worse on the international level. While there is often at least an expressed concern about denominational divisions within nations, there seems to be very little concern expressed about denominational divisions between nations. On this level, there seems to be a widespread failure to even think about the issue at all, with some even voicing opposition to the idea that all the national Reformed churches ought to be united under one binding ecumenical council. But to fail to take the logic of presbyterian church government to the international level, and instead to settle there for an independent view of things, is ultimately to betray presbyterian church government. On this level, as well, a sense of "peace in Zion" is helped along, I think, by the existence of advisory, non-binding organizations (like the ICRC) which facilitate the different churches working together in certain areas short of full organic union. And this in spite of the fact that denominations like the OPC have expressed an interest in working for worldwide organic unity (see, for example, this very good article on the subject of church unity).
In another place, I have discussed the implications that come from having divided denominations. Each denomination, by not being unified with another, is declaring that only it has formally recognized de jure authority and therefore de jure existence as a church (while division is compatible with a de facto recognition of the Body of Christ in differing denominations). I think that raising the issue of an ecumenical council helps to bring this fact out clearly, and so it is something I want to raise and emphasize. Basically put, we can ask the question, Who would you invite to an ecumenical council? An ecumenical council would be a binding synod of the whole church throughout the world. So one's answer to this question reveals whom one considers to be a part of the catholic church worldwide, considered de jure. To not be invited to take part, with full voting privileges, in an ecumenical council is to be "unchurched," to be rejected as being a part of the universal Christian church, considered de jure. So who would we invite to an ecumenical council?
The fact is that all the Presbyterian/Reformed denominations that exist would invite only officers and members in their own denominations to be fully voting members in such a council. This is because they would recognize that to invite others would be to give them power over their own denominations, as their own respective denominational general assemblies and synods would be subject to the binding authority of this higher council. But the very reason they are separate denominations is that they do not want to give those outside their denominations any power within their denominations, so they will not invite them to be fully voting members of the ecumenical council. But while they might be able to ignore or put behind them the full implications of their decisions to remain separate from each other while going about their ordinary business, the act of calling an ecumenical council (or even considering doing such in a thought experiment) will make these implications impossible to ignore. When denominations refuse to be in full organic communion with each other, they are not merely deciding to co-exist peacefully and happily as different parts of a larger church. They are declaring everyone but themselves to be excluded from the universal, catholic, visible Church of Christ, considered de jure. Obviously, such a declaration is something that is extremely weighty and not at all to be taken lightly. To claim to be the one, holy, catholic, and apostolic church, de jure, is a tremendous claim. Those who make such a claim dare not make it unless they are absolutely certain (at least to the extent that such matters allow) that it is true. What Reformed churches today really often want to do is to think of the de jure catholic church as existing in all the different denominations as they work together in their divided state. Such an idea of the church may work within the structure of congregational/independent church government, but it is not at all tenable within the context of presbyterian church government.
So, let me ask these question of all the different Presbyterian/Reformed denominations out there: Who would you invite to an ecumenical council? And are you prepared to deal with and accept and defend with full consciousness the implications of your answer? Do you have a right to exist as a separate denomination, with all that that claim entails? Or are you schismatic, and in need of repentance? What are you going to do to help seek both the purity and the unity of the universal Church of Christ (both de jure and de facto)? If you do want to make the claim that you have the right of separate existence, are you doing what you can to promote the purity and unity of the church on an international scale? Are you looking at all the other nations as mission fields, where you have an obligation to work for the existence and maintenance of de jure catholic churches (however it is best to go about doing this in particular places)? Are you taking the pains that need to be taken to deal with these many mission fields? Are you working to reform churches that are divided from you as you have opportunity? Are you working to do all you can, while upholding the whole of your duty, to make things easier on other denominations who might seek union with you? If you decide that you don't have a basis to make the claim that your denomination is the one, holy, catholic, and apostolic church worldwide, considered de jure, what are you going to do to end your schismatic separate existence? Which denomination ought you to be joining, and what steps are you currently taking to make that happen within a reasonable period of time (understanding that it may take some, limited amount of time to make such a transition)? If you are engaged in holding some doctrinal deviation or some unbiblical practice, or some other practice that unnecessarily hinders unity, how are you going to go about reforming this obstacle to unity?
UPDATE (10/5/12): See here and here for related blog articles.
UPDATE 9/2/13: Samuel Hudson makes some interesting comments about calling an ecumenical council in his 1649 book, A Vindication of the Essence and Unity of the Church-Catholick Visible, pp. 215-216. (This is an excellent book overall, by the way, arguing for formal, visible, catholic unity in the whole church.) After spending a good amount of time arguing for the legitimacy and binding nature of an ecumenical council, he says this:
But because there are so many superstitions, errours, and heresies in the Asian, African, European and American Churches, as M. A and M. S in their defense, p. 92, do take notice of . . . yet I say for these things' sake, I should be very tender in defining (as the case now standeth) what Churches, or how farre the visible Churches may with convenience or safety enter into actual combination, lest the truths of God, or the liberties or the more sound and pure Churches, should be prejudiced thereby.
Hudson is writing before what I call the "age of denominationalism" really dawned (which dawning I tend to place around 1690--recognizing, of course, a bit of subjectivity in this). It was not yet clear at this point that the Protestant and Reformed churches were going to end up definitively splintered into a myriad of separated denominations. Therefore, he is still contemplating at this time the calling of an ecumenical council that would include a variety of Protestant churches. However, we can see that the age of denominationalism is almost upon us in his reasons for hesitation at the idea of calling such a council. The various Protestant churches have become so divided and disparate already that Hudson doubts that it really makes sense anymore to call a council. Errors have become established, and more orthodox churches are already functioning separately from less orthodox ones. It was, perhaps, already too late to heal the divisions of Christendom by means of an ecumenical council. Once the church came to be in a divided state, it would have been foolish to go back and pretend it hadn't happened by calling such a council. From that time on, the only way forward would be dialogue between already-separated churches. And if this was already becoming so in Hudson's day, how much more in ours! The Reformed churches of today need to stop living in denial of the divided state of Protestantism, accept the schisms that exist without pretending that de jure catholic unity still exists between the various Protestant and Reformed denominations, and engage in serious soul-searching and dialogue in order to help bring the churches into greater agreement and so move closer to restoring the de jure unity of the de facto visible church.
UPDATE 10/15/14: Here is another article which asks a similar question: What would your church do if some other church invited it to a mutually-binding council?