In his 2014 post What is Porneia to a 1st Century Jew, Scott McKnight wrote:
The term porneia is a Greek term that has two basic meanings:
Sex with a prostitute; prostitution.
Sexual immorality in general.
For the “in general” definition of porneia, McKnight looks to Leviticus 18. He returned to the subject in a 2015 post, here.
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But what does porneia mean? There are two basic meanings: (1) sexual relations with a prostitute or, in a more general sense, (2) sexual immorality, which for a Jew refers to prohibited degrees of intercourse. When you double-click on the term porneia, then, it takes you to Leviticus 18.
…. So, while porneia can be a sweeping generalizing term referring to any kind of sexual immorality, for the Jew there was an established list of what was meant. If one wants specifics, no better listing can be found than in Leviticus 18. In fact, the importance of this chapter for defining what porneia would have meant for a 1st Century Jew cannot be exaggerated. Leviticus 18 was for the Jewish world of Torah observance God’s covenant gift to the Israelites (18:1-2) that both clarified how to live and set them apart from pagans. Thus, the chapter overtly distances Israelites from the Egyptians and Canaanites (18:3, 24-28, 29-30) in prohibiting sexual relations with:
- close relatives (18:6),
- parents (18:7) and the spouses of parents (18:8),
- siblings (18:9, 11),
- spouses of one’s children or their children (18:10),
- aunts [and uncles] or their spouses (18:12-14),
- children by law (18:15),
- sisters-in-law [and brothers-in-law](18:16),
- a woman and her daughter and her children (18:17),
- sister in law (18:18),
- women during menstruation (18:19),
- neighbor’s wife (18:20),
- same-sex relations (18:22),
- and animals (18:23).
The categories at work in what a Jew in the 1st Century meant by porneia were shaped by the Torah, and that means Leviticus 18.
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In his commentary on Matthew in the Reading the New Testament series, David Garland followed the same train of thought. In his discussion of the “Matthean exception” – the prohibition of divorce “except for porneia” (Matthew 5:32, 19:9), Garland writes about one possible line of interpretation that doesn’t focus on adultery breaking the marriage:
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An increasing number of scholars have therefore argued that the Greek word porneia can refer to sexual sins in general and does not mean “unchastity” in this instance. It refers instead to marriage within the forbidden degrees of kinship (Lev 18:6-18, 20:11-12, 14, 17, 19-21; Deut 22:30, 27:20, 22-23).
The marriage of Herod Antipas to Herodias, the former wife of his brother, would have been such an unlawful union (it was not a levirate marriage since she had a child by her former husband, who was also still alive; Deut 25:5-10); and it prompted John the Baptist’s bitter attack against them (14:3-4).
The word that specifies adultery (moicheia, verb forms, moicheuo, moicheaomai) is used in 5:27-28, 32, but not in the exception clause. The two words are distinguished from one another by the Evangelist, since they appear together in the same list of vices in Matthew 15:19 (see also 1 Cor 6:9, Heb 14:4).
No special technical term for incest was current in Greek before the Byzantine era, and the word porneia could serve to refer to it. Paul expresses his shock that a man was living with his father’s wife and calls it porneia (1 Cor 5:1; see Lev 18:6-8; Testament of Reuben 1:6, 4:8; Testament of Judah 13:3; Jubilees 16:5; 20:5).
The Jerusalem Council ruled that if gentile converts wanted to have fellowship with Jewish Christians, they need not become circumcised but must abstain from “pollution of idols, what is strangled, blood and porneia” (Acts 15:29; also 21:25). Porneia is usually translated “unchastity,” but why specify that gentiles need to refrain from unchastity as a minimal requirement for fellowship with Jewish Christians? Chastity was not something that was or is optional for Christians. Since the other requirements in the list refer to restrictions found in the Holiness code in Leviticus 17-18 (meat offered to idols, 17:8-9; blood, 17:10-12; strangled meat, 17:15), it would seem likely that porneia refers to sexual contact with a partner prohibited in Leviticus 18:6-18.
If porneia refers to what a Jew would consider to be a forbidden union, then Matthew may have added this exception because the infusion of gentile converts within the Christian community posed a practical dilemma. The predicament was this: if a gentile Christian was married, and in the eyes of Jewish Christians the relationship was incestuous (see Paul’s vehement reaction in 1 Cor 5:1), what was to be done? The answer: divorce was required. Why? Because God could not possibly have joined together two who were forbidden to one another. God could never have recognized this marriage. Therefore, Matthew’s church, in a mission setting quite different from that of Jesus, adapted Jesus’ repudiation of divorce to make clear that this did not apply to a situation that they believed required divorce. Jesus’ prohibition of divorce applies only to valid marriages, and the exception clause applies only to quite exceptional cases – marriage within forbidden degrees of kinship – and does not provide an escape hatch for those husbands whose wives have committed adultery.
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However, Garland still favors adultery – sexual unfaithfulness in marriage – as the simplest understanding of Matthew’s intent.
Likewise, a quick review of porneia in the Septuagint finds the majority of uses referring to literal or figurative prostitution, adultery or other dishonorable sexual behavior in general, and not specifically to Leviticus’ list of prohibited partners.
It seems to me that for the apostolic church, the prohibited relationships listed in Leviticus 18 constituted only a subset of the broader category of porneia.