We can confirm that this is the FPCS's position also by looking at the Free Presbyterian Catechism, written up by the FP church itself (a new edition having just been issued in 2013). I have pasted relevant portions from that catechism below, combined with a little commentary of my own (in red).
106 Q. What is meant by Christ’s Church being Catholic?
A. The word Catholic means Universal, which teaches us that the Church of Christ is one in all nations.
There is only one Body of Christ, and so that Body (the church) is one in all nations, throughout all the earth. Here we see articulated the biblical and presbyterian view of the unity and catholicity of the church. There are not many "bodies of Christ" divided up into separate and independent portions in different nations or other localities.
108 Q. What do we mean by the term “the visible Church”?
A. The visible Church is made up of all those throughout the world that profess the true religion, together with their children (Acts 2:39).
108 Q. What do we mean by the term “the visible Church”?
A. The visible Church is made up of all those throughout the world that profess the true religion, together with their children (Acts 2:39).
Again, we see the worldwide or international character of the church--not just in its "invisible" aspect but in its "visible" aspect as well. There is only one visible church on the earth, and so it is one in all nations.
128. Q. Are there other forms of Church government adopted by men professing to follow the New Testament?
A. Yes, there is the Independent or Congregational form of government in which congregations are not in subjection to superior courts, and frequently no distinction is made between teaching and ruling elders.
112 Q. How should we describe the Free Presbyterian Church?
A. The Free Presbyterian Church of Scotland should be described as a branch of the visible Church in the world.
A. The Free Presbyterian Church of Scotland should be described as a branch of the visible Church in the world.
The language of "branch" suggests that there are other branches. The FPCS is not itself the totality of the visible church in the world.
114 Q. What are the other Presbyterian Churches in Scotland?
A. The other Presbyterian Churches in Scotland today are the Church of Scotland, the United Free Church, the Free Church, the Free Church (Continuing), the Reformed Presbyterian Church, the Free Presbyterian Church of Ulster, the Associated Presbyterian Churches and the International Presbyterian Church[17]
114 Q. What are the other Presbyterian Churches in Scotland?
A. The other Presbyterian Churches in Scotland today are the Church of Scotland, the United Free Church, the Free Church, the Free Church (Continuing), the Reformed Presbyterian Church, the Free Presbyterian Church of Ulster, the Associated Presbyterian Churches and the International Presbyterian Church[17]
Here are some other branches of the visible church in the nation of Scotland. The Catechism focuses in upon Scotland because the FPCS exists mostly in Scotland and considers itself by Scottish national constitution the rightful official church of the nation of Scotland. But there are, of course, other branches of the visible church in other nations as well, such as the Orthodox Presbyterian Church, which exists primarily in the United States.
A. Yes, there is the Independent or Congregational form of government in which congregations are not in subjection to superior courts, and frequently no distinction is made between teaching and ruling elders.
In presbyterianism, church government is collegial, and so congregations are not independent. They are subject to superior courts. As Charles Hodge articulated it, "The Presbyterian doctrine on this subject is, that the Church is one in such a sense that a smaller part is subject to a larger, and the larger to the whole." In independency, by contrast, congregations are not subject to larger binding church councils.
148 Q. What is schism?
A. Schism is a breach of the union and communion that ought to exist within the visible Church in doctrine, government and worship (1 Cor. 12:25; Rom. 16:17).
140 Q. What is its Supreme Court of the Free Presbyterian Church?
A. The Synod is the Supreme Court of the Free Presbyterian Church and regulations for its affairs, and those of all the other Church courts, are to be found in the Church’s Manual of Practice.
The highest court recognized by the FPCS is its own Synod. This highlights its separation from other denominations, as there are no mutual courts uniting the FPCS to any other denomination and so no recognized mutual submission with any other denomination.
141 Q. Is the Free Presbyterian Church opposed to union with other Churches?
A. No, the Free Presbyterian Church encourages biblical union with any Church in Scotland or overseas provided that there is a unity in doctrine, worship, government, discipline, and practice.
A. The Synod is the Supreme Court of the Free Presbyterian Church and regulations for its affairs, and those of all the other Church courts, are to be found in the Church’s Manual of Practice.
The highest court recognized by the FPCS is its own Synod. This highlights its separation from other denominations, as there are no mutual courts uniting the FPCS to any other denomination and so no recognized mutual submission with any other denomination.
141 Q. Is the Free Presbyterian Church opposed to union with other Churches?
A. No, the Free Presbyterian Church encourages biblical union with any Church in Scotland or overseas provided that there is a unity in doctrine, worship, government, discipline, and practice.
Of course the FPCS encourages biblical union with other churches. This follows from its commitment to a presbyterian understanding of the unity and government of the church. In a presbyterian system, the visible church throughout the earth is to function in formal unity and with collegiality in its government. Denominational independency is forbidden.
142 Q. But should we not for the sake of brotherliness overlook differences and join with other Churches?
A. No, it is not brotherly to overlook important principles in doctrine, worship, government, discipline, and practice and so unless there is common ground on all these, any union would be at the expense of truth (Rom. 16:17, 18; 2 Thess. 3:6).
142 Q. But should we not for the sake of brotherliness overlook differences and join with other Churches?
A. No, it is not brotherly to overlook important principles in doctrine, worship, government, discipline, and practice and so unless there is common ground on all these, any union would be at the expense of truth (Rom. 16:17, 18; 2 Thess. 3:6).
Although unity is a requirement, that unity must be in the truth. There is therefore a warrant and a duty to refrain from uniting with churches that have compromised the faith and practice of the church in matters where Scripture has spoken clearly. Here, the catechism articulates the FP church's opposition to latitudinarianism.
143 Q. Can Christ’s prayer “that they all may be one” (John 17:21, 23) justify creating a single Church from every Church that professes to be Christian, irrespective of its doctrine?
A. No, because this would make it contradict the clear testimony of Scripture that Church unity can only be in the truth (Eph. 5:11; 1 Cor. 1:10; Eph. 4:13-16; 1 Tim. 3:15).
143 Q. Can Christ’s prayer “that they all may be one” (John 17:21, 23) justify creating a single Church from every Church that professes to be Christian, irrespective of its doctrine?
A. No, because this would make it contradict the clear testimony of Scripture that Church unity can only be in the truth (Eph. 5:11; 1 Cor. 1:10; Eph. 4:13-16; 1 Tim. 3:15).
Same comments as just above.
144 Q. Are there any in the visible Church who are not true believers?
A. In every Church that professes Christ there will be a mixed company of true believers and others who are not true believers.
144 Q. Are there any in the visible Church who are not true believers?
A. In every Church that professes Christ there will be a mixed company of true believers and others who are not true believers.
This articulates the distinction between the "invisible" and the "visible" church.
145 Q. May there be such declension in a professing Christian Church that it becomes no longer Christian?
A. The Scriptures speak of a “synagogue of Satan” in spite of its profession (Rev. 2:9 and 3:9). Christ calls his people to come out of Babylon, which is the name given to the apostate Church of Rome in Scripture (Rev. 18:4).
145 Q. May there be such declension in a professing Christian Church that it becomes no longer Christian?
A. The Scriptures speak of a “synagogue of Satan” in spite of its profession (Rev. 2:9 and 3:9). Christ calls his people to come out of Babylon, which is the name given to the apostate Church of Rome in Scripture (Rev. 18:4).
Churches can become so corrupted that they should be considered "apostate." Among these is the Romanist church, which has vitiated the core of the gospel by its false doctrine and worship.
146 Q. When should individual believers separate from the fellowship of others?
A. The Scriptures enjoin believers to withdraw themselves from those who are professed brethren and who walk disorderly (2 Thess. 3:6), so when men have so rejected sound doctrine, right government, and discipline, or have introduced superstitious worship, or are maintaining a schismatic position, and when an orderly correction of these evils fails, then believers are to separate from such.
A. The Scriptures enjoin believers to withdraw themselves from those who are professed brethren and who walk disorderly (2 Thess. 3:6), so when men have so rejected sound doctrine, right government, and discipline, or have introduced superstitious worship, or are maintaining a schismatic position, and when an orderly correction of these evils fails, then believers are to separate from such.
Christ has given the keys of discipline to his church in order to preserve purity in doctrine and practice. When believers fall into sin in various ways, if they cannot be reclaimed through an "orderly correction," they are to be cut off from the visible body until they repent. This applies not just to church members, but to church leaders as well. If church leaders are called to repent and refuse to do so, are then cut off by discipline (in the name of Christ) from the visible church, but yet continue to maintain that they continue to possess ecclesiastical legitimacy, the result will be the creation of two church bodies (denominations) where before there was only one. In this case, continuing denominational separation becomes a duty. (This happened, for example, when the FP church separated from the Declaratory Act Free Church in 1893.)
The concept of "schism" is introduced here, which will be discussed further below. It is important to note here that we are to separate from those who "are maintaining a schismatic position." That is, we are to refrain from union with those who are schismatics. If there are professed church leaders who are schismatic, we are not to join with them by recognizing and submitting to their professed authority, for they are to be regarded as cut off from the fellowship of the church (and therefore also, obviously, from office in the church) until they cease to be schismatic.
147 Q. When is it lawful to break ecclesiastical union through separation?
A. Unity is an absolute duty and therefore the only lawful reason for separation is when one is compelled unavoidably to sin in order to maintain the bond of union. In this case the sin of schism is made by those compelling to sin. Up until this point any separation would be unjust schism since one may still testify against corruptions in the Church and use all lawful means to have them removed.
"Unity is an absolute duty." Of course. This follows, again, from the presbyterian nature of the church. Since unity within the visible church is an absolute duty, we have a moral obligation to preserve that unity unless continuing in that unity requires us to sin, in which case we are warranted and have a duty to separate. For example, when the former Free Church of Scotland adopted the Declaratory Act (see link above), this altered the constitution of the church and thus required sin of all its officers. Therefore, the fathers of the FP church had no choice but to separate in the name of Christ from the Free Church.
Such a separation is warranted because those who have forced the separation by requiring sin must be disciplined by the church according to Christ's command. Denominational separation is thus an act of discipline, by which the faithful party cuts the erring party off from the church and refuses to acknowledge its continuing legitimacy and authority. It entails a charge of schism from the faithful party to the erring party, and the erring party is henceforth (until it repents) to be regarded as schismatic.
If separation is engaged in when sin is not required to maintain unity, this separation is unwarranted and is thus itself a schismatic act.
148 Q. What is schism?
A. Schism is a breach of the union and communion that ought to exist within the visible Church in doctrine, government and worship (1 Cor. 12:25; Rom. 16:17).
The visible church, being one in all the earth, has a duty to manifest that oneness by unity in its doctrine and worship (and practice), and in its government. That is why unity is an absolute duty. It is why "the Free Presbyterian Church encourages biblical union with any Church in Scotland or overseas." Schism--that is, the unwarranted division of one part of the visible church from another part--is thus a sin.
A question arises here: What is the status of a "schismatic church"? Should it be considered a part of the visible church or not? I think the answer is "yes" and "no." In a de facto sense, schismatic churches are parts of the visible church because they profess Christianity. (It is in this sense that the FPCS claims to be one branch among others within the visible church.) That is precisely what makes schism possible and so heinous. We do not speak of the church being in "schism" from the body of Buddhists in the world precisely because Buddhists do not profess to be parts of the Body of Christ at all. There can only be schism between parts of the de facto visible church. On the other hand, we are not to have formal fellowship with schismatic churches. We are not to join formally with them and submit to their authority. They do not possess formal legitimacy as churches. Thus, they can be said to be out of the visible church considered de jure. Historian James Walker, I think, expresses this nuance well as he attempts to articulate how the Scottish Presbyterian churches of the 1600s viewed schismatic churches: "It is not clear to me what, according to this view, was the exact position of a schismatical Church. If it had the main truths, it was still a Church,--a Church, I think they would have said, in concreto and materially, and salvation work might go on there; but formally and in abstracto, it could not be recognized as a Church, or communion held with it as such." A distinction of this sort seems the only way to preserve the nuances articulated here in the catechism. John Calvin articulated a similar distinction in his comments on the status of the Church of Rome in his Institutes: "In one word, I call them churches, inasmuch as the Lord there wondrously preserves some remains of his people, though miserably torn and scattered, and inasmuch as some symbols of the Church still remain - symbols especially whose efficacy neither the craft of the devil nor human depravity can destroy. But as, on the other hand, those marks to which we ought especially to have respect in this discussion are effaced, I say that the whole body, as well as every single assembly, want the form of a legitimate Church." Of course, none of this is to say that all schismatic churches are on the same level in terms of how far they have departed from orthodoxy in doctrine and practice.
Can we have any Christian fellowship with those in schismatic churches? Clearly, we cannot have any kind of fellowship which would negate our position regarding the schismatic nature of those in schism. But if we can recognize (as I think we can, and as is implied in the above discussion) that the Body of Christ is manifested in various ways (though not legally) among schismatics at least in some circumstances, and that there are grounds for a charitable hope that many even among schismatics are truly regenerate Christians (members of the invisible church), then it seems to me (though this question is not addressed by the catechism) that we can engage in various kinds of informal fellowship with schismatics, so long as we do not engage in any fellowship that would condone their schism or negate our formal separation.
149 Q. What is the duty of Churches in Scotland who profess to represent the Reformed Church?
A. All Presbyterian Churches in Scotland claiming to represent the Reformed Church and who have caused or who maintain schisms contrary to the avowed Westminster Standards are bound to repent and to return to purity in doctrine, worship, government and discipline. The Free Presbyterian Church of Scotland is not guilty of schism and claims to be the true heir of the Reformed Church of Scotland in doctrine, worship, government and discipline. While she certainly does not claim perfection, she maintains that all Churches in Scotland should unite around her constitution and testimony.
Here, the catechism makes explicit in the context of the nation of Scotland the conclusions already implicit above. Since the FP church has a right to exist, and to exist for now separately from other denominations in Scotland, it follows that the other Scottish churches are in schism and thus need to "repent and to return to purity in doctrine, worship, government and discipline." The FP church, of course, does not hold that itself is in schism, for that would be to reject its own legitimacy and authority and thus undermine its very claim to have a basis for separate existence. Because the visible church has a duty to be unified, all churches in Scotland have a duty to unite around the FP testimony and thus with the FP church.
Of course, it is evident from the entire context that these same conclusions apply to the FP church's relationship with churches in other nations as well. The catechism zones in to focus on the churches of Scotland because of its unique connection to Scotland, but the catechism has acknowledged that the visible church of Christ is and has a requirement to be "one in all nations," and thus, as it articulated earlier, biblical union is to be sought with churches in Scotland "and overseas" (and in nations other than Scotland but not overseas as well--that is, England). The FP church's commitment to the international unity of the visible church in manifested, for example, in its existing congregations and presbyteries in other nations, such as its congregation in Santa Fe. TX, in the United States. It has been said that these congregations in other nations are the seeds of national churches in these nations. The 2011 FP Religion and Morals Committee Report (p. 11) put it this way: "The Committee believes that this Presbyterial structure is the model for Church government in every nation and that our presence as a Church in other nations implies that we aim at fully established Presbyterian structures within these nations." Thus, the FPCS does not recognize, for example, the OPC in the US as constituting the de jure church in the US, but has begun the process of building its own "Presbyterian structures" within the US.
Our look through the FP Catechism's discussion of the church and church unity has confirmed what we already knew from the implications of the FP's confession of presbyterian church government: The FPCS believes itself warranted to continue for now in denominational separation from the OPC, and this means that the FPCS thinks of the OPC as a part of the de facto visible church but also as a schismatic sect speaking de jure. There are other ways this conclusion can be confirmed as well, but we have now fulfilled my intentions for this particular article.
For more, see here and here.
UPDATE 3/10/15: I thought I'd add a few quotations from the FP website further confirming what the FP Catechism says about the the oneness of the visible church throughout the world (not just in Scotland), the concomitant duty of unity, and thus the schismatic nature of any denomination (in Scotland or in any other nation) which is not in formal communion with the FPCS.
First of all, from the "What We Stand For" section of the FP website. Under the heading of "Reformed in Church Practice" the website affirms that the FP church professes an "[a]ffirmation of Presbyterianism as the Scriptural system of church government to the exclusion of all others" and an "[a]cknowledgment that whilst all who profess the true religion should seek ecclesiastical union in one visible church, the Church’s testimony to Biblical truth should never be diluted: therefore our separate stance from other denominations is our unavoidable duty at the present time" (links in original).
Then, from the "Frequently Asked Questions" section of the website, we have this comment in response to the question, "Are You Ecumenical?":
See also this statement on "Our Separate Stance," which includes this comment:
UPDATE 3/10/15: I thought I'd add a few quotations from the FP website further confirming what the FP Catechism says about the the oneness of the visible church throughout the world (not just in Scotland), the concomitant duty of unity, and thus the schismatic nature of any denomination (in Scotland or in any other nation) which is not in formal communion with the FPCS.
First of all, from the "What We Stand For" section of the FP website. Under the heading of "Reformed in Church Practice" the website affirms that the FP church professes an "[a]ffirmation of Presbyterianism as the Scriptural system of church government to the exclusion of all others" and an "[a]cknowledgment that whilst all who profess the true religion should seek ecclesiastical union in one visible church, the Church’s testimony to Biblical truth should never be diluted: therefore our separate stance from other denominations is our unavoidable duty at the present time" (links in original).
Then, from the "Frequently Asked Questions" section of the website, we have this comment in response to the question, "Are You Ecumenical?":
Being a Presbyterian church we believe in the unity of congregations in a Presbyterian structure. We do not believe in the spurious unity of the modern “ecumenical movement” which minimises doctrinal difference between the Protestant churches and which is leading towards reunion with Roman Catholicism under the pope. We believe in the unity of all Spirit-taught, born-again, believers in Christ throughout the world, and that this should be expressed ecclesiastically in Presbyterian church government.
See also this statement on "Our Separate Stance," which includes this comment:
Accordingly, conduct giving the impression that there is no obstacle to association with other Churches undermines the necessity for a separate position and is therefore inconsistent with loyal adherence to the Free Presbyterian Church, and is consequently disapproved of by this Church.