It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father's wife.
All Commentaries on 1 Corinthians 5:1 Go To 1 Corinthians 5
George Leo Haydock
As the like is not among the heathens. This seems to have been the crime of incest, that he took the wife of his father yet living. See 2 Corinthians vii. 12. (Witham)
St. Chrysostom, Theod., think, that this incestuous person was one of the chiefs of the schism which then reigned in Corinth. This man, say they, was a great orator, with whose eloquence the Corinthians were enchanted, and therefore dissembled a knowledge of his crime, public as it was. The apostle having proved to them the vanity of all human learning, in the preceding chapter, now attacks the incestuous man, and exposes to their view the enormity of his crime. (Calmet)