Jesus prays that His disciples “might be matured into one” (osin teteleiomenoi eis hen, John 17:23). It’s a pregnant phrase.

Unity requires maturity, the willingness to deal with those who differ, the willingness to face conflict without anxiety. Think of marriage.
Maturity is nurtured by the difficult work of unity. When we face conflict without fear, we grow, most especially in faith. Think of marriage.

Division is childish. It’s childish to retreat into our safe places, where everyone is like us.

Division rules in the childish world of the old covenant (cf. Galatians 4), the world split in two by the cut of circumcision, a world of tribes and tongues and nations and peoples. To be content with division is to revert to that old world. Division is a form of Judaizing.

We cannot have mature Christianity in the midst of our divisions, because maturation is maturation toward unity. So long as we remain divided, we remain children.