In Paul: Fresh Perspectives, N. T. Wright makes an astute observation about church unity:
We who live with the disunities of the late-modern church can easily forget that church disunity was a fact of life from almost the very beginning — from, at least, the dispute between Hebrews and Hellenists reported in Acts 6. Almost always it had, right from the start, at least an element of ethnic or tribal sympathy at war with the baptismal call to die to old identities and to come alive in and to the new one, the solidarity of the Messiah.
He’s riffing on an old, well established theme. The occasional nature of the NT letters, just like the polemical edge of the creeds, reminds us that most theological formulations are thrashed out in a context of conflict.
This ought never dull our passion for church unity — Paul avidly pursues it throughout 1 Corinthians as a precondition for the call to cross-shaped living.
But I suppose it should temper our efforts with realism.