What else was evident in the Corinthian congregation besides the sin of believers?

Besides the sin of believers, malice and other forms of wickedness were evident in the Corinthian congregation. This wickedness functioned as leaven permeating that local assembly, and the group was plagued with almost every sin imaginable, while God nevertheless kept them in a place of growth.

Les explains that while the issue was still the sin of believers in that local congregation, they were not the only ones falling far short. He points out that malice and other forms of wickedness were also evident, describing it as leaven permeating that little congregation. It was a wonder it survived, since this group was plagued with almost every sin one could think of. Yet God did not give up on them; He kept them in a place of growing and growing, and Paul eventually came to a place where he was surely proud of the Corinthians.

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.