In a post titled "Church Unity", Lane Keister writes:

The only other point that needs to be brought up here is the unspoken assumption on Wilson’s part that church unity is a fundamentally organizational goal. One can see this with the pejorative statements “ungodly denominational system,”(p. 117) and “denominations are a necessary evil” (p. 118). Why is the unity of the body of Christ organizational? If there are believers in just about every Christian denomination, then there is Christian unity. Period. Christian unity is a (S)spiritual unity (see Ephesians 4:1-6, where nowhere is it implied that it has to be an organizational unity). Paul does not say that there should be Christian unity. He says there is unity. If that passage applies at all today, then the unity is in no way, shape, or form organizational. I am by no means saying that the cottage industry of denomination fragmentation is a good thing. Many denominations are formed for wrong reasons. But if denominations are inherently evil, then the Reformation was wrong to start new denominations (of course, they argued that the Roman Catholics were the schismatics, since they were the ones abandoning truth). If we want to avoid conflict with our Baptist brothers, because they will not baptize infants, and we will, then we had better worship apart for the sake of unity. In fact, we have greater unity with the Baptists by worshipping apart than we would if we were constantly fighting over the proper subjects of baptism. Should we strive for eliminating unnecessary denominations? Absolutely. There is no particular reason why the PCA and the OPC should be two separate denominations. Not really. Of course it would require a lot of work. But I think we are duty bound to seek such unification. However, because the principle of denominations is abused does not mean that the principle itself is evil. People are different, and there are different worship styles, as well as different theological beliefs. So true Christian unity is trans-denominational.

Consider Lane's arguments. Here is the first:

(1) If there are believers in just about every Christian denomination, then there is Christian unity.

(2) There are believers in just about every Christian denomination.

(3) Therefore, there is Christian unity.

Not only is the apodosis of (1) a non sequitur, but (1) makes disunity impossible, and implies that the unity of the Church is unaffected by schism.

His next argument is:

(4) Ephesians 4:1-6 refers to the "unity of the Spirit".

(5) Nowhere in this passage is it implied that it has to be an organizational unity.

(6) Therefore Christian unity is a (S)spiritual [not organizational] unity.

Notice the explicit equivocation in (6) between Spiritual (i.e. Spirit-wrought), and spiritual (i.e. not organizational). The move from (4) to "Spirit-wrought" in (6) would be fine. But the move from (4) and (5) to "spiritual" [and not organizational], is a non sequitur on account of an equivocation between 'Spirit' and 'spiritual', and because the move from (5) to "spiritual" [and not organizational] in (6) is an argument from silence.

His third argument is:

(7) Paul does not say [in this passage] that there should be Christian unity.

(8) Paul says [in this passage] that there is unity.

(9) Therefore, if this passage applies at all today, then the unity is in no way, shape, or form organizational.

(10) This passage applies today.

(11) Therefore, Christian unity is in no way, shape, or form organizational.

Line (9) is a non sequitur; it does not follow from (7) and (8).

In comment #19 Lane replies to Jonathan Bonomo:

And you are misreading Ephesians 4. By your argument, the denominations around today cannot be part of the body of Christ, since it has to be a visible manifestation. You have the same problem, by the way, even if you have organizational unity, since each individual church is separate from another church. What difference does it make if separate churches happen to be in the same denomination or a different denomination? Are they any less part of the body of Christ? The body of Christ is plainly the whole church, and unless you want to disenfranchise thousands upon thousands of churches from being part of the body of Christ, you ***cannot*** define the body of Christ in this way.

Lane's first argument in this comment is the following:

(12) The denominations around today are all part of the body of Christ

(13) If visible unity were necessary, then the denominations around today would not be part of the body of Christ

(14) Therefore visible unity is not necessary.

Line (13) is a non sequitur, because it assumes that parthood is all or nothing.

His next argument in this comment is:

(15) Every particular church is part of the body of Christ

(16) Every particular church would still be a separate body, even if they were all in the same denomination.

(17) Therefore, the "one body" of Eph 4 must refer to a spiritual (not organizational) unity.

This argument is a non sequitur as well, because it assumes that being [geographically] separate bodies is incompatible with being one visible body by way of hierarchical organization.

If we could take a survey of gnostics regarding the nature of Church unity, how would their position (on this subject) differ from Lane's? Lane's position entirely spiritualizes the unity of the Body of Christ. It treats the Body of Christ as did the Docetists, as a spirit only seeming to have a body. But bodies are hierarchically organized. And the Body of Christ is a "Body". And so the Body of Christ is hierarchically organized.

"... those who arbitrarily conjure up and picture to themselves a hidden and invisible Church are in grievous and pernicious error: as also are those who regard the Church as a human institution which claims a certain obedience in discipline and external duties, but which is without the perennial communication of the gifts of divine grace, and without all that which testifies by constant and undoubted signs to the existence of that life which is drawn from God. It is assuredly as impossible that the Church of Jesus Christ can be the one or the other, as that man should be a body alone or a soul alone. The connection and union of both elements is as absolutely necessary to the true Church as the intimate union of the soul and body is to human nature." (Satis Cognitum, 3)