Paul had written an earlier
letter to the Corinthians (εγραψα υμιν εν τη επιστολη) in
which he had instructed them to avoid immoral people. They had misunderstood
him to mean that they should avoid non-Christian moral offenders. Paul corrects
their misconception in w. 9—13 and explains that it is those who claim to be
Christians (τις
αδελφος ονομαζομενος) and yet commit such
offences whom they must avoid. He urges them not to associate with ('be mingled
together with' - συναναμιγνυσθαι)
these people in vv.. 9-11 and then cites a decretal formula which occurs
frequently in Deut. (James T. South, “A Critique of the ‘Curse/Death’ Interpretation
of 1 Corinthians 5.1-8,” New Testament Studies 39, no. 4 [October 1993]:
554)