Porneia (πορνεία) is the broad NT term for sexual sin outside of God-ordained marriage. It covers fornication (sex outside of marriage), adultery, prostitution, incest, and by extension, all sexual activity that violates God's design. The English word 'pornography' derives directly from this Greek root. It is consistently listed among the gravest threats to the body, the church, and the individual's union with Christ.
The NT treatment of porneia is comprehensive and serious. It is included in every major sin list (Mark 7:21; 1 Corinthians 6:9; Galatians 5:19; Revelation 21:8). Paul's argument in 1 Corinthians 6:18-20 is unique: while other sins are 'outside the body,' porneia is a sin against one's own body — because the body is a temple of the Holy Spirit and was created for union with Christ, not with prostitutes. The Jerusalem Council's decree (Acts 15:20, 29) listed abstaining from porneia as one of the few requirements for Gentile believers — showing its universal gravity. Revelation uses porneia metaphorically for spiritual unfaithfulness to God (the 'great prostitute' of Babylon in Revelation 17-18).
The severity with which the NT treats porneia is not cultural prurience but theological conviction: the body matters because it is destined for resurrection (1 Corinthians 6:14), because it is a temple of the Holy Spirit (6:19), and because sexual union creates a 'one flesh' bond (6:16) that, when applied to Christ, should be an image of holy union rather than a profanation. Paul's command is not a list of prohibitions but a vision of the body's dignity and destiny. The antidote to porneia is not just avoidance but the fullness of Spirit-filled identity: 'You are not your own, for you were bought with a price. So glorify God in your body' (6:19-20).