I do not pray for these alone [the Apostles], but also for those who will believe in Me through their word; that they may be one . . .that they also may be one in Us . . . that they may be one just as We are one . . . that they may be made perfect in one . . . (John 17:20, 21,22, 23).
In the High Priestly prayer of our Lord, we find Christ earnestly interceding for the unity of all Christians (understood as those who believe in Christ according to apostolic witness).
Has God answered the prayer of His Son?
When we consider the apparent fragmentary condition of the Church, we may be tempted to answer, “No. Jesus’ desire for Christian unity is unfulfilled.” But we should resist this temptation. It is my conviction that God has in fact preserved the unity of His people: one flock with one Shepherd (John 10:16).
The Church is unified. But what is the nature of its unity?
Let’s begin by specifying what it isn’t. The nature of Christian unity is not ecclesiastical. That is, the one people of God meet all over the world in various local groups or churches. The one Church gathers in thousands of churches which belong to a myriad of denominations and/or associations.
There is diversity. But that which unites the one Church is greater than that which would divide her.
Let’s now consider what the unity of the one Church is.
According to Jesus, our unity is doctrinal. That is, Christ prays for “those who will believe in Me” in agreement with the “word” of the Apostles. We often hear the mantra: Doctrine divides. True enough, Christians do not see eye-to-eye in all matters of faith and practice.
But surely we understand the much deeper truth that doctrine unites. Regarding doctrine, Augustine famously quipped: “in essentials unity, in non-essentials liberty, in all things charity.”
The question now becomes: Is that which unites us (essential Christian truths) greater than that which divides us (non-essentials). I believe it is. It is the essence of our faith—the essentials—which CS Lewis envisions in Mere Christianity.
Ever since I became a Christian I have thought that the best, perhaps the only, service I could do for my unbelieving neighbors was to explain and defend the belief that has been common to nearly all Christians at all times (from the preface to Mere Christianity).
There are cardinal truths which all Christians in all times believe.
In addition to the doctrinal unity of all believers, we find the spiritual. We are spiritually joined to all Christians of all the ages. Jesus speaks of our spiritual communion as being twofold.
First, He says all Christians of all the ages are “one in Us.” We are in the Father and Son.
Second, the Father and Son are in us: “I in them, and You in Me; that they may be made perfect in one” (John 17:23). Christians of all the ages are the one Body of Christ, the one Temple of God.
Thus within the biblical Christian faith, doctrinal/spiritual unity is deeper than surface level diversity. And we can recognize this fact without compromising—in any sense—our distinctives. In other words, we can affirm our unity and not deny our diversity.
There is one body and one Spirit, just as you were called in one hope of your calling; one Lord, one faith, one baptism; one God and Father of all, who is above all, and through all, and in you all (Ephesians 4:4-6).