This episode continues to describe the inherent advantages of Paul's addressing believers in churches as "saints" as opposed to addressing his letters to a "church." Paul's last 4 letters don't even mention the word "church" in the intro. The main advantage of the word "saint" is that it invokes a significant amount of Christian theology. A "saint" is one who is accounted righteous based on the righteousness of Christ. Christ's merit alone, made available through His sacrificial death and resurrection, is the ground of sainthood. Additionally, sainthood connotes one who is set aside for God's purposes. The word "church" COULD be interpreted as the outward visible church without reference to the Biblical basis of participation in that church. Many note that nominal believers often point to their participation in the visible church without reference to the necessity of repentance and faith in Christ. The episode finally notes that Paul experienced firsthand working with "false brethren," so-called believers who were never saints to begin with. They identified with the visible church but were NOT saints. Nominal believers and tares hide behind denominational banners, identification with a visible church, but are not yet part of the church that Christ is building.
