“Nothing can be clearer, of course, than that the conception of its unity enters fundamentally into the New Testament doctrine of the Church.” (B. B. Warfield, “True Church Unity: What It Is,” p. 299)
The Priority of Christian Unity
The pursuit and maintenance of unity among confessing Christians is a clear, compelling and central biblical imperative which cannot be ignored or refused without quenching the Spirit’s presence and power among us. As R. B. Kuiper rightly notes, “The Word of God teaches the unity of the church unmistakably, repeatedly and emphatically. It is no exaggeration to assert that this is one of the most outstanding teachings of the New Testament.”[1] 
I make this simple point largely because many Christians (in my view) acknowledge a good deal of the various components that go into the makeup of a truly biblical unity, yet assign the doctrine far too low a status on their scale of competing priorities.
It is not enough to correctly comprehend the doctrinal contours of unity; one must also acknowledge the stunning value the New Testament writers assign to it in the redemptive economy of God. To give an illustration of this distinction, take the doctrine of justification as expounded by Paul in Galatians. One could, hypothetically, agree entirely with Paul regarding the content of justification by faith apart from works, yet at the same time disagree with the profound priority it holds for him—a priority that can be seen, of course, in his “anathema” upon all who deny it (Galatians 1:6-9). A person could conceivably share in common the fact of justification by faith with Paul but not the value he placed upon it. I argue that this is precisely how many Christians today relate to the biblical teaching on unity in the church. While often agreeing on what it demands, they wrongly relegate it to a subordinate, secondary place in the lives of believers. The profound importance of unity in the church is not felt as it should be. This allows us to feel far more comfortable with our woeful disobedience and failure, apart from our ever actually having to repent of it. This is convenient to be sure, yet it can only provide the sort of peace that finds its origins in the covering up of wounds, not in the actual healing of them (Jeremiah 6:14, 8:11).
The compelling and pervasive[2] New Testament witness could not be more different in either tone or emphasis. For these apostolic writers, unity among the people of God was of the very essence of their faith and of what God was after in a divisive, shattered world that He was nonetheless pursuing. The one Creator God had redeemed a people to exist as one in Christ and in the Spirit, reflecting His image. As the Father and the Son are one (10:30), so also we are to be one (17:11, 21-23). This oneness is at the core of both the identity and the mission of the body of Christ. Unity is not to be regarded, by any means, as optional or merely secondary in the economy of the gospel.
It was so central to Jesus’ own ethical vision that a great deal of his final prayer on the night before his death was concerned with it. Unity consistently and repeatedly arises in both the doctrinal and the practical exhortation sections of the various New Testament letters. It saturates every section of the New Testament in one way or another. Unity in the church is simply not understood correctly unless it is perceived to be a first-order priority for all believers.[3] It is a communal practice in which the gospel is perpetually at stake.
The conclusion is unavoidable that we have not properly grasped the biblical doctrine of unity until our passion runs as high for its appearance and maintenance as it did for Jesus and his apostles. Therefore, we must continually mourn for its absence, actively repent of our complicity in the divisions in the church, and eagerly and sacrificially work for the attainment of the goal that both Jesus (John 17) and Paul (Ephesians 4:11-16) labored so severely for. We must adopt this perspective of John Calvin, apparent in his 1552 letter, responding to Thomas Cranmer’s invitation to a conversation on the reunification of the churches of Europe:
“I wish indeed it could be brought about that men of learning and authority from the different churches might meet somewhere and, after thoroughly discussing the different articles of faith, should, by a unanimous decision, hand down to posterity some certain rule of faith . . . . As to myself, if I should be thought of any use, I would not, if need be, object to cross ten seas for such a purpose. If the assisting of England were alone concerned, that would be motive enough for me. Much more, therefore, am I of opinion that I ought to grudge no labor or trouble, seeing that the object in view is an agreement among the learned, to be drawn up by the weight of their authority according to Scripture, in order to unite widely severed churches.”[4]
Calvin speaks of crossing ten seas for the sake of the church’s unity. For many Christians today, an hour or two over coffee each week to fellowship and pray with the members of another congregation feels like an unbearable sacrifice, and thus we avoid such encounters with a clear conscience.
Holy Father, arise, and awaken your slumbering people from their selfish sleep through your life-giving Spirit, for the sake of your sacred Son. Amen.
[1] The Glorious Body of Christ, pp. 41-42
[2] Cf. Psalm 133:1, John 10:16, 11:52, 17:1-26, Acts 1:14, 2:44, 4:32, Romans 15:5-7, I Cor. 1:10, 10:17, 12:12-26, Ephesians 2:14-16, 4:1-16, Philippians 1:27-2:2, 4:2-3, Colossians 3:14-15, etc.
[3] I have heard N. T. Wright say recently that in his upcoming big book on Paul—the 4th volume in his Christian Origins series—he will argue that unity is the central theme of Paul’s theology. I eagerly look forward to hearing his case!
[4] Letter to Thomas Cranmer in 1552. A. Basil Mitchell notes that “Calvin was mastered by the vision of a world-wide church one in Christ, and he regarded it as one of the great ends of his earthly mission to promote its realization.” (as cited in John Armstrong, Your Church Is Too Small)