Whose sin was Paul dealing with in the Corinthian congregation?
Paul was dealing with the sins of believers within the Corinthian congregation itself. That local church was plagued by malice, wickedness, and almost every sin imaginable, a leaven permeating the group. Though they fell far short, God did not abandon them; He kept them in a place of growth.
Les explains that the sin Paul addressed was not outside the church but among believers in that local congregation. They were not the only people falling far short, yet malice, other forms of wickedness, and a leaven were permeating that little group. Les notes it is a wonder it survived, since they were plagued with almost every sin, but God did not give up on them; He kept them growing.