In these verses, the apostle deals with a particular situation involving sin in the congregation. He identifies a man who was guilty of having sexual relations with his father’s wife. The wording here would indicate a stepmother.
However, Paul does not deal with the man himself. In fact, he says that he has already judged in the matter (vs. 3). The man was guilty, and stood condemned before God.
Here Paul is addressing the Corinthians lack of action. He tells them that they should have already removed the man from their midst, and called their refusal to do so an act of pride (cf. vs. 2, 6).
Here Paul reveals the congregational action that is required when an individual is in rebellion to God. By Christ’s authority the congregation is to come together, and mark and banish him as one unworthy of Christian fellowship. Other reasons for this action follow in later verses, but in verse 5 he states one of the most compelling ones, “that his spirit may be saved in the day of the Lord Jesus.”
Brethren, congregational discipline saves men’s souls.