The question of unity among Christians is easily and often misunderstood. It is typically reduced to affectionate or friendly feelings toward people I know who attend my congregation and agree with me a lot. That is the unity of a club — it could easily be the unity of a cult. But Christian unity is Christ:
Christian community means community through Jesus Christ and in Jesus Christ. There is no Christian community that is more than this, and none that is less than this. Whether it be a brief, single encounter or the daily community of many years, Christian community is solely this. We belong to one another only through and in Jesus Christ.
What does that mean? It means, first, that a Christian needs others for the sake of Jesus Christ. It means, second, that a Christian comes to others only through Jesus Christ. It means, third, that from eternity we have been chosen in Jesus Christ, accepted in time, and united for eternity.
First, Christians are persons who no longer seek their salvation, their deliverance, their justification in themselves, but in Jesus Christ alone. They know that God’s Word in Jesus Christ pronounces them guilty, even when they feel nothing of their own guilt, and that God’s Word in Jesus Christ pronounces them free and righteous, even when they feel nothing of their own righteousness. Christians no longer live by their own resources, by accusing themselves and justifying themselves, but by God’s accusation and God’s justification. They live entirely by God’s Word pronounced on them, in faithful submission to God’s judgment, whether it declares them guilty or righteous
Dietrich Bonhoeffer, Life Together and Prayerbook of the Bible, ed. Gerhard Ludwig Müller, Albrecht Schönherr, and Geffrey B. Kelly, trans. Daniel W. Bloesch and James H. Burtness, vol. 5, Dietrich Bonhoeffer Works (Minneapolis, MN: Fortress Press, 1996), 31.