The historical understanding of the nature and mission of the church is elusive to say the least. People who write about Biblical Christianity, and early Christianity seem to assume that early Christianity is in a purer form, and that the Apostles practiced and believed what the writer feels is correct. We suffer from people who make an idol of beginnings. This is made all the more difficult as a quote from the second or third century (Such as Cyprian’s famous: “There is no salvation outside the church.”) can mean something fully different to a member of the persecuted church than it does to a church that enjoys a privileged position in society. Very often our best guesses of how the church saw itself is how it responds to those who see things differently.
Cyprian’s church was persecuted, and one of the most important heretical groups was the Novatians. The policy of Orthodox Christians was to allow those who were afraid of persecution and did not accept martyrdom under the state, but instead to say “Caesar is Lord” to repent and return to the Church. The Novatians felt that Lapsi should never be let back. One could not claim loyalty to Christ one day, and loyalty to empire the next, and then expect the Church to forgive him. Cyprian wrote against those who felt that the church was too eager to forgive, and created their own fellowship intended to exclude the impure. Cyprian is a moderate who is credited with inviting sinners back, but calling all Christians to confess. My guess is that the mission of the church, as it was in the last period of persecution, was to help people live a difficult life, and to call for mercy when they failed live up to the highest ideals by dying to themselves.
Over time Christianity was accepted, and over time the merger of the ideas of Church and state made it so that in many ways the mission of the church was to create good citizens, and to maintain public order. The mission of the church switched from subverting to supporting the state. While there were likely buildings devoted to Christian worship before persecution ended, church buildings and public visibility replaced whispered meetings in small apartments. The church became a public instead of a suppressed institution.
In all of this, one can say that the church’s mission remained constant — the church seeks salvation from sin through the person and ministry of Jesus Christ. Though many modern Christians speak of salvation as if the only thing they need saved from is punishment, the damage of sin is more than punishment. It is likely that the Church sought the salvation of society by means of a good influence. Lest we forget, the preaching of Christians was influential in ending the cruelty of the Colosseum. While we might complain that the church was corrupted by the state, the church also made real attempts to bring a type of salvation to earth.