In my discussions with various people about presbyterian church government and its implications for the unity and collegiality of the church (see here for example), I sometimes encounter people claiming that it is all very well and good that the church should be unified and function collegially, and that denominationalism is antithetical to the very nature of the church and its government, but that one cannot insist on such things in our current non-ideal climate. Sure, the collegial functioning of church government is ideally supposed to be an important way in which the church maintains its unity and purity, but the ideal simply can't exist right now. For example, the OPC cannot right now embrace full unity with the RPCNA and function collegially with them in terms of government--such as by holding a common council to come to terms with doctrinal differences such as the dispute over exclusive psalmody. The OPC cannot do this because it would have to compromise its own doctrinal commitments to do so, such as its commitment to allow the singing of uninspired hymns in public worship. A denomination ought never to compromise its doctrinal commitments for the sake of unity when it believes those commitments to be biblical. So we'll just have to settle for a non-ideal denominational division between de jure true churches at this time and hope and work for better in the future.
So the argument goes, and it sounds plausible on the surface. But when examined just a little more closely, it makes no sense. For one thing, does God give the church permission to ignore his prescriptions for how the church is to function simply on the basis that "we live in non-ideal times"? All times this side of eternity are "non-ideal." Do we get to dispense with other commands of God when we feel the times are not right for them--like prayer, Bible study, the preaching of the gospel, love to neighbor, etc.? Only God's Word can tell us when we can make exceptions to his general commands, and where in God's Word has he given us the right to divide the unity of the church and ignore the authority of fellow presbyters and church courts on the grounds that we think them less orthodox in doctrine or practice than ourselves? As James Durham put it, "by way
of precept there is an absolute necessity of uniting laid upon the
church, so that it falls not under debate ‘Whether a church should
continue divided or united . . . more than it falls under
debate whether there should be preaching, praying, keeping of the
Sabbath, or any other commanded duty; . . . [T]hat men should
by agreement state a division in the church, or dispense therewith and
prefer the continuing of division, as fitter for edification than union,
we suppose is altogether unwarrantable."
The reply might be made that a faithful denomination cannot unify with all other denominations, because Christ has also commanded the church to keep the faith pure, which can't be done if it does not remain separate from groups which have distorted it in some way. This is quite true, but it brings us to another absurdity of the argument under examination. The argument maintains that de jure churches ought to remain separate from other less pure de jure churches in order to protect the purity of the faith, and that therefore there cannot at this time be unity and a collegial exercise of church authority between such divided denominations, such as would be manifested by having common councils, etc. But this argument seems to forget one of the main purposes for which Christ commanded collegial and conciliar authority in his church, which was to preserve the purity of the church within its unity. Thus, instead of being a reason for de jure churches to avoid participating in common binding councils, existing contradictions in doctrine and practice are the best reasons for holding such councils. In fact, a non-ideal situation of churches contradicting each other in doctrine and practice is actually the most ideal situation for holding church councils, for the collegial and conciliar use of church authority is a primary means appointed by Christ for the church to use to help maintain its unity by dealing with the divisions in doctrine and practice that threaten it. Collegial church authority is intended to help preserve the purity of the church within its unity. To neglect this means of the sanctification of the church and instead, contrary to Christ's command, to willingly separate the de jure church into isolated factions that refuse to respect each others' authority and deal with their differences is not only not the way Christ has ordained to preserve the purity and unity of the church but is certainly one of the best ways to ensure the continuation of disunity and impurity within it. This argument and course of action, then, is like a sick man who refuses to go to the doctor because his circumstances are non-ideal--i.e. he is sick. When he gets better, he says that that will be the time to go.
Therefore, this argument clearly fails as an excuse to continue to keep the de jure church in a divided state. Denominationalism is never permitted, and it is never the path towards the healing of the church. In terms of a consistent presbyterian practice, the division of two churches into two distinct denominations can only mean that the two denominations are rejecting each others' legality and authority as de jure churches, having pronounced sentence upon each other and cut each other off. Any attempt to justify the severance of de jure churches from each other while continuing to attribute de jure status to them entails an abandonment of biblical presbyterianism.
I've dealt with this argument in other places as well, such as here and here.
UPDATE 2/6/15: From my book on this subject, a couple of analogies that provide further illustration of why the "non-ideal time" argument doesn't work:
#1. You're absolutely right that it would be a great thing for all the different denominations, and especially the Reformed denominations, to be united. This is definitely the ideal we should be seeking. But we need to have proper nuance in our thinking. Just because, say, the OPC and the PCA are not united in the ideal way, it doesn't follow that they are not united at all, or that they are rejecting each others' de jure legitimacy and authority. Husbands and wives can be separated to some degree in times of marital trouble without being fully and finally divorced. So churches might be separated in ways that are not ideal without it necessarily implying that they completely reject each other as legal churches.
The problem with this argument is that it fails to acknowledge the real essence of the problem. It is absolutely crucial that all actual nuances be properly recognized, but it is also crucial that we avoid inventing nuances where they do not in fact exist. Imagine that Frank and Sarah are a married couple having problems, and Frank comes to you and says this: “You know that Sarah and I have been having problems in our marriage. Here's what we've decided to do: We're going to live separately, avoid intimate relations, have separate bank accounts, and feel free to see other people. Although this is not ideal, we think it will be good for our relationship. We'll still be husband and wife, but in a sort of recovery mode.” You will probably respond by informing Frank that what he has in mind is not any kind of marriage relationship at all, whether he chooses to call it that or not, because he and Sarah will be living in such a way as to deny the very essence of what it means to be married. To be married involves more than just a name; there are certain essential characteristics that have to be there to lay just claim to the name. Husbands and wives can't see other people, they have to actually spend time with each other, etc. Without these things, they can't claim the name “marriage” for their relationship.
Similarly, the relationship between two legal churches in a presbyterian system involves certain essential characteristics, and if these characteristics are not there, the churches can't claim to recognize each others' legality. As we've seen, active, legal elders have an inherent right to function as parts of larger church courts, and church courts have an inherent right to function as parts of the universal governing body of the catholic church. The very recognition of legality when it comes to ecclesiastical authority involves formal and binding mutual submission and accountability. When denominations are separate from each other, that mutual submission and accountability are not there. For Denomination A to refuse to engage in mutual submission and accountability with Denomination B while still choosing to say they attribute legal authority to Denomination B is a mere pretense—a name without the thing. Another parallel that might help is to think of the sphere of civil relations. Imagine someone saying, “Sure, I acknowledge the legal authority of the United States government! I just don't think I have any obligation to obey any of their laws and policies, pay taxes, show respect, etc.” Such alleged “acknowledgment of legal authority” would be merely a sham; there is no real acknowledgment there are all, for the essence of what such acknowledgment means is denied.
The OPC article on biblical unity, cited earlier, uses the term “sinful disunity” to describe denominational division. It does so precisely because denominational unity between the legitimate churches of Christ is not just some nice ideal to work for someday; it is a moral requirement that necessarily always exists between all legitimate churches, a requirement they cannot abandon without sin. Denominational division, by its very essential nature, involves a rejection of legitimacy in terms of legal authority. It is certainly true that churches can exist in a state of tension with each other without an implied mutual rejection of legitimacy. Temporary states of discipline can exist between elders and elders, or between elders and members, etc., without a violation of the essential unity of the church. What can't consist with that essential unity, however, in a presbyterian system, is a settled, permanent division in which the separated denominations refuse to submit to each other.