His concluding comments on 2:11-22, where he's been talking about how Christ tore down the old divisions (Jew & Gentile), only to have us create new "dividing walls of hostility" -- racism, nationalism, tribalism, social status, clericalism, denominationalism, etc...
"What is offensive to Christ is offensive also, though in a different way, to the world. It hinders the world from believing in Jesus. God intends his people to be a visual model of the gospel, to demonstrate before people's eyes the good news of reconciliation. But what is the good of gospel campaigns if they do not produce gospel churches? It is simply impossible, with any shred of Christian integrity, to go on proclaiming that Jesus by his cross has abolished the old divisions and created a single new humanity of love, while at the same time we are contradicting our message by tolerating racial or social or other barriers within our church fellowship. I am not saying that a church must be perfect before it can preach the gospel, but I am saying that it cannot preach the gospel while acquiescing in its imperfections.
"We need to get the failures of the church on our conscience, to feel the offence to Christ and the world which these failures are, to weep over the credibility gap between the church's talk and the church's walk, to repent of our readiness to excuse and even condone our failures, and to determine to do something about it. I wonder if anything is more urgent today, for the honour of Christ and for the spread of the gospel, than that the church should be, and should be seen to be, what by God's purpose and Christ's achievement it already is -- a single new humanity, a model of human community, a family of reconciled brothers and sisters who love their Father and love each other, the evident dwelling place of God by his Spirit. Only then will the world believe in Christ as Peacemaker. Only then will God receive the glory due his name."
from John Stott, The Message of Ephesians, pp. 111-112