sexual wrongdoing: sexual activity outside the bounds the Old Testament law sets for marriage
This is the ordinary New Testament use of the word, and the one the standard reference works settle on. It is a broad label that gathers up adultery, prostitution, sex before marriage, incest, and other forbidden sexual acts under a single heading, measured against the marriage boundaries drawn by the law of Moses. The early Christians did not invent that breadth from nothing. In ordinary Greek the word group was narrow and commercial, tied to prostitutes who were usually bought slaves; it described what the seller did, so a man who visited a brothel was thought to have done nothing wrong by it. Greek-speaking Jews stretched the word far past that, until it could name almost any sexual conduct the law forbade, and the Christian movement stretched it further still.
Because the word is a basket rather than a single act, its exact contents shift with the setting. Most often it is simply general sexual sin, and it stands first or near the front of the New Testament lists of vices. But a writer can load it with sharply specific content: when Paul confronts a man living with his father's wife, the word names that one forbidden union and nothing vaguer. The senses below mark out that range, from the wide default to two places where the precise reference is genuinely argued over.
The English words we reach for all pull in their own directions. "Fornication" narrowed in later church usage to sex before marriage; "sexual immorality" is broad but lets the reader supply a modern definition of what counts. The word itself keeps pointing back to the law's marriage rules rather than to any one culture's sense of decency.
Nuances
Whether the word in the Jerusalem decree means the forbidden unions of Leviticus 18 or sexual immorality connected with pagan worship.
- contestedIt refers to the marriages within forbidden kinship degrees in Leviticus 18, since the four prohibitions of the decree track the law's rules for the foreigner living in Israel in Leviticus 17 to 18.; Richard Bauckham, "James and the Gentiles (Acts 15.13-21)," in The Book of Acts in Its Palestinian Setting (Eerdmans, 1995), 415-480; Joseph A. Fitzmyer, The Acts of the Apostles (Anchor Bible 31; Doubleday, 1998), 556-558
- contestedIt refers to sexual immorality bound up with pagan temple practice, alongside idol food and improperly slaughtered meat.; Ben Witherington III, The Acts of the Apostles: A Socio-Rhetorical Commentary (Eerdmans, 1998), 460-467
What πορνεία means in Jesus's exception for divorce.
- majorityBroad sexual immorality: divorce is permitted where the marriage has been broken by sexual unfaithfulness of any kind. The dominant reading in the commentary tradition.; R. T. France, The Gospel of Matthew (NICNT; Eerdmans, 2007), 204-209; D. A. Carson, "Matthew," in Expositor's Bible Commentary (Zondervan, 1984), 8:413-419
- minorityA forbidden union within the kinship degrees of Leviticus 18, so the clause is not a true exception, since such unions were never valid marriages.; Joseph A. Fitzmyer, "The Matthean Divorce Texts and Some New Palestinian Evidence," Theological Studies 37 (1976): 197-226
- contestedThe question cannot be settled on the words alone; Matthew's clause is too compressed to decide between the readings.; W. D. Davies and Dale C. Allison, A Critical and Exegetical Commentary on the Gospel According to Saint Matthew (ICC; T&T Clark, 1988-97), vol. 1, at 5:32
What πορνεία refers to in the divorce exception of Matthew 5:32 and 19:9, where the parallels in Mark, Luke, and 1 Corinthians 7 contain no exception at all.
- majorityBroad sexual immorality, so divorce and remarriage are permitted where sexual unfaithfulness of any kind has broken the marriage. The dominant view in modern commentary.; R. T. France, The Gospel of Matthew (NICNT; Eerdmans, 2007), 204-209, 717-722; Craig S. Keener, ...And Marries Another: Divorce and Remarriage in the Teaching of the New Testament (Hendrickson, 1991); Donald Hagner, Matthew 14-28 (WBC 33B; Word, 1995)
- minorityAdultery specifically, the wife's extramarital intercourse; though it is objected that Matthew has the ordinary word for adultery available and uses it elsewhere.; Hauck and Schulz, TDNT 6:592; William Loader, "Did Adultery Mandate Divorce? A Reassessment of Jesus's Divorce Logia," New Testament Studies 61 (2015): 67-78
- minorityA forbidden union within the kinship degrees of Leviticus 18, drawing on Jewish legal texts such as the Damascus Document, so the clause is no real exception because such unions were never valid marriages.; Joseph A. Fitzmyer, "The Matthean Divorce Texts and Some New Palestinian Evidence," Theological Studies 37 (1976): 197-226; Markus Bockmuehl, Jewish Law in Gentile Churches (T&T Clark, 2000)
- minorityUnchastity discovered during the betrothal period, on the model of Joseph and Mary; though Matthew 19 is explicitly about marriage rather than betrothal.; Abel Isaksson, Marriage and Ministry in the New Temple (Gleerup, 1965)
- contestedThe exegetical question cannot be resolved on the words alone; the clause is too cryptic to decide, and is most likely Matthew's own redactional addition to an originally absolute saying of Jesus.; W. D. Davies and Dale C. Allison, A Critical and Exegetical Commentary on the Gospel According to Saint Matthew (ICC; T&T Clark, 1988-97), vol. 1, at 5:32; Ulrich Luz, Matthew (Hermeneia; Fortress)