David Janzen wrote an article in 2001 that was published in the Journal for the Study of the New Testament on the meaning of porneia in Matthew 5:32 and 19:9. In Matthew’s account of Jesus’ teaching on marriage and divorce, Jesus only allows for divorce in cases of porneia. But what does this refer to? It’s usually translated as “adultery,” but the Greek word for adultery is moicheia. Porneia has a wider semantic rate, referring to a range of sexual sins. It can be used of adultery, incest, pre-marital sex, etc.
Janzen argues that Jesus’ use of porneia is best understood from the cultural context. In Jesus’ day, some argued that divorce could be obtained for any reason, while others argued that one must have just cause. All agreed, however, that the husband only had to return the wife’s dowry to her if had just cause for divorcing her. Jesus sided with those who taught that the only justification for divorce was a just cause. He identified that cause as porneia. What does porneia refer to? Is he referring to a wide range of sexual sins? Janzen argues that the cultural context makes it likely that porneia refers specifically to something akin to adultery. Why didn’t Matthew use moicheia, then? The most likely explanation is that Jesus did was not limiting the exception to sex with another person during the marriage (adultery), but was also including sex with another person during the betrothal period (which, in Jesus’ day, was as legally binding as marriage).
Check out the article: Porneia in Mt 5_32 and 19_9–Janzen
David Janzen, “The Meaning of Porneia in Matthew 5:32 and 19:9: An Approach From the Study of Ancient Near Eastern Culture,” in Journal for the Study of the New Testament, 2001; 23; 66; available from http://jnt.sagepub.com/cgi/content/abstract/23/80/66.