For Christians, the norm of sexual behavior is simple: fidelity within marriage, chastity without it. Because of the current debate over same-sex marriage, that norm has been clarified by making explicit the traditional understanding of marriage as a lifelong heterosexual union. This norm is rooted in the creation narrative (Genesis 1:27, 2:24) and reaffirmed by Jesus Christ (Matthew 19:4-5, Mark 10:6-8) and the Apostle Paul (1 Corinthians 6:15-16, Ephesians 5:31).

New Testament authors use the word porneia specifically in reference to prostitution (1 Corinthians 6:15-18) and broadly in reference to any violation of the norm, whether premarital sex (1 Corinthians 7:2), adultery (Matthew 5:32), or incest (1 Corinthians 5:1). Because of the prevalence of sexual immorality in Greek culture, the church taught Gentile converts to repent of porneia (Acts 15:20, 29; 21:25). Paul listed it first among “the works of the flesh” (Galatians 5:19), most likely because of its prevalence. He further stated that the practice of porneia – meaning prostitution specifically – alongside other sins such as adultery and homosexuality, disinherited a person from receiving the kingdom of God (1 Corinthians 6:9).

With this background in mind, let’s turn to 1 Corinthians 5:1-2:

It is actually reported that there is sexual immorality among you, and of a kind that does not occur even among pagans: A man has his father’s wife. And you are proud! Shouldn’t you rather have been filled with grief and have put out of your fellowship the man who did this?

In this passage, porneia refers specifically to incest. A man in the Corinthian church was engaging in sexual intercourse with “his father’s wife,” that is, his stepmother. Rather than being horrified by this flouting of the norm, a norm which in the case of incest even the otherwise sexually lax Greeks happened to share, the Corinthian Christians were “proud.” It’s not clear whether they were proud of this man’s exercise of sexual freedom or proud of how tolerant they were. Either way, Paul described the proper emotional response as “grief” and the appropriate action as excommunication.

What is our reaction to sexual sin?

In my experience, modern Christians tend toward the extremes of intolerance and tolerance. On the one hand, some Christians elevate sexual sins above other sins. On the other hand, other Christians turn a blind eye toward porneia, except when it involves child sexual abuse, incest, and adultery. This tolerance arises from the notion that premarital sex or homosexual activity, or the use of pornography, are trivial.

Neither extreme is right. God cares about how we use our bodies, including how we use our bodies sexually. The biblical norm of marriage leads toward human flourishing both in this life and the life to come. The worldly value of porneia leads to human languishing both in this life and the life to come. When people flourish, we should rejoice; when they languish, we should grieve.

The church’s task in the present age is to help people understand the connection between the norm and human flourishing.