1 Corinthians 5:1

"Immorality" is a general translation of the Greek word porneia, which means fornication, specifically sexual relations with a forbidden mate. The precise offense in this case was sexual union with the woman who had married the man’s father (cf. Matthew 5:27-28; Matthew 5:32; Matthew 15:19; Matthew 19:9; Mark 7:21). Had she been his physical mother other terms would have been more appropriate to use. Evidently the woman was his step-mother, and she may have been close to his own age.

"The woman was clearly not the mother of the offender, and probably (although the use of porneia rather than moicheia [adultery] does not prove this) she was not, at the time, the wife of the offender’s father. She may have been divorced, for divorce was very common, or her husband may have been dead." [Note: Robertson and Plummer, p. 96. Cf. Barclay, p. 49.]

The verb translated "to have" (present tense in Gr.), when used in sexual or marital contexts, is a euphemism for a continuing relationship in contrast to a "one night stand" (cf. 1 Corinthians 7:2). This man and this woman were "living together." Since the man is the object of Paul’s censure, it seems that the woman was not in the church.

"The word porneia (’sexual immorality’) in the Greek world simply meant ’prostitution,’ in the sense of going to the prostitutes and paying for sexual pleasure. The Greeks were ambivalent on that matter, depending on whether one went openly to the brothels or was more discreet and went with a paramour [lover]. But the word had been picked up in Hellenistic Judaism, always pejoratively, to cover all extramarital sexual sins and aberrations, including homosexuality. It could also refer to any of these sins specifically, as it does here. In the NT the word is thus used to refer to that particular blight on Greco-Roman culture, which was almost universally countenanced, except among the Stoics. That is why porneia appears so often as the first item in the NT vice lists, not because Christians were sexually ’hung up,’ nor because they considered this the primary sin, the ’scarlet letter,’ as it were. It is the result of its prevalence in the culture, and the difficulty the early church experienced with its Gentile converts breaking with their former ways, which they did not consider immoral." [Note: Fee, The First . . ., pp. 199-200.]

The leaders of Israel and the early churches regarded fornication of all kinds as sin to avoid (Leviticus 18:8; Deuteronomy 22:30; Deuteronomy 27:20; Acts 15:20; Acts 15:29; Acts 21:25). If the guilty man’s father was still alive and married to the woman, adultery would also have been involved. Most interpreters have concluded that this was a case of incest rather than incest and adultery. If Paul had been living under the Mosaic Law, he should have prescribed the death penalty for both the guilty man and the woman (Leviticus 18:8; Leviticus 18:29), but he lived under the New Covenant and advocated a different penalty (1 Corinthians 5:5). As depraved as Greek culture was, even the pagans looked down on incest, and Roman law prohibited it. [Note: Johnson, p. 1236.]