More from Hauerwas, from his commentary on Matthew:
Any community of Jesus which wants to be invisible is no longer a community that follows him. Christians, however, are tempted to become invisible, justifying their identification with the surrounding culture in the name of serving the neighbor. One of the names given such invisibility is Constantinianism, a term that describes the strategy of Christians when they become an ally of Caesar.
John Howard Yoder makes the striking observation that after the Constantinian shift, the meaning of the word "Christian" changes. Prior to Constantine it took exceptional conviction to be a Christian. After Constantine it takes exceptional courage not to be counted as a Christian. The establishment of Christianity had the ironic result of making paganism morally compelling... Before Constantine, Christians assumed as a matter of faith that God was governing history even in the person of the emperor, but they knew that God was present in his church. After the Constantinian establishment, Christians knew that God was governing the world in Constantine, but they had to take it on faith that within the nominally Christian mass there was a community of true believers. No longer could being a Christian be identified with church membership, since many "Christians" in the church had not chosen to follow Christ.