Before Jesus went to the cross for us. He prayed that we would become perfectly one with each other, with the Father and with Himself. WE COULD ANSWER HIS PRAYER. We could "Make every effort to pursue the unity of the spirit — there is only one body, and one Spirit" Eph 4: 3. But we don't, because we are not really sufficiently Reformed, or more importantly sincerely committed to God's sovereign redemptive plan. We really don't quite believe in the Headship of Christ over the church.
We sincerely ask Jesus to answer our many prayers. The one prayer request that Jesus makes — which we have the capacity to answer — we essentially ignore. Yet, we are happy and content with the Protestant penchant for schism, and we happily embrace "denominationalism". Our own form of subscription affirms our stand against what Jesus is asking for. I have often heard excuses that our disunity is simply a result of sinfulness. So we decide, to simply go on sinning.
So what kind of unity are we talking about here? or what kind of unity is Jesus praying for? I would suggest that it is not "ecumenism", which is typically understood as a bringing together of "institutions" into one big institution or denomination — so sound teaching is water down. I am sure that is not what Jesus had in mind. He refers to a relational unity — a deep fellowship and communion that it defines the Oneness of the triune God. Their are three differnet persons in the Godhead. Yet, they are so close in their fellowship with each other that they are One God. In is a similar way there is only ONE BODY — we just somehow think we can pretend it is not so.
This unity is more than just fellowship. It is a shared mission and function. "That the world may know"
When all of the CR churches in Kalamazoo meet with other evangelical churches and worship together, a genuine pursuit of this unity has begun. When they begin to develop strategies for ministering to all the domestic violence victims, and begin divorce care together, and have a city wide training conference, then they have come closer to answer Jesus' prayer. When they do everything they can together to cause the gospel to ring out everywhere — then they will have become serious about the heart and desire of Jesus' request.
While the Belhar confession is mostly about racial reconciliation, Article 3 gets at the Biblical teaching about pursuing the unity of the body. This is not just ecumenical gobbledeegook, it is one of the most essential teachings of a true Reformed faith.