The doctrine of the church which we have found in John seems to me to call for some revisions of our conventional ecclesiology.

The time-honored notae ecclesiae, the marks of the church, are preaching of the word and the administration of the sacraments. Says Calvin: “Wherever we find the word of God purely preached and heard, and the sacraments administered according to the institution of Christ, there, it is not to be doubted, is a Church of God.”

[However] if we are on the right track in these studies, then surely the preeminent mark of the church is engagement in mission to the world.

If mission defines who Christ is, and if Christ sends us as he was sent, then mission defines who we are. We can preach the word and celebrate the sacraments in all solemnity, propriety, and purity, but if we are doing nothing to speak the words of God and to do the works of God in the world, if we have no concern for liberation, justice, compassion, and peace, can we claim the name of church? I think not.

– A Sense of Mission: Guidance From the Gospel of John by Albert Curry Winn