Fornication is a term used in the Bible for any sexual misconduct or impure sexual activity that occurs outside of the bounds of a marriage covenant. Fornication is also applied symbolically in the Bible to the sins of idolatry and apostasy, or the abandoning of God.
The word fornication comes from the Greek term porneia (from which we get our English word pornography) and is often linked with adultery in the Bible. It is a general term for sexual immorality. Fornication includes adultery, which is the act of a married person engaging in sexual intercourse with someone other than his or her spouse. But fornication also involves engaging in any kind of sexual relations before marriage or between two people who are not married. For instance, in the King James Version of 1 Corinthians 5:1, fornication is used twice to describe a sexual sin that was being tolerated by the church: a man was sleeping with his father’s wife.
In a list of horrendous sins in Romans 1:29, the apostle Paul includes fornication, referring to all kinds of sexual immorality. Jesus mentions fornication in a list of corrupting sins that come from within a person’s heart: “For from the heart come evil thoughts, murder, adultery, all sexual immorality [fornication], theft, lying, and slander” (Matthew 15:19, NLT; see also Mark 7:21).
The sin of fornication violates the seventh commandment (Exodus 20:14), which was intended to safeguard the integrity of the family and the marriage union. God designed sex for marriage, and marriage to be a holy, prized, and honored institution. The Bible calls husbands and wives to keep themselves exclusively for one another or face God’s judgment: “Marriage is to be honored by all and the marriage bed kept undefiled, because God will judge the sexually immoral and adulterers” (Hebrews 13:4, CSB). Condemnation of sexual immorality is unanimous in Scripture. Those who persistently indulge in fornication will not inherit the kingdom of heaven (1 Corinthians 6:9).
Abstaining from fornication was one of four conditions required of the Gentiles to be accepted into the early church by the Jerusalem conference: “Abstain from meats offered to idols, and from blood, and from things strangled, and from fornication: from which if ye keep yourselves, ye shall do well” (Acts 15:29, KJV).
The Bible instructs believers to run from every kind of sexual sin, including fornication: “Let there be no sexual immorality, impurity, or greed among you. Such sins have no place among God’s people” (Ephesians 5:3, NLT; see also 1 Corinthians 7:2; 1 Thessalonians 4:3).
According to Paul in 1 Corinthians 6:18, sexual sin is unique in that it is a sin against one’s own body. This idea is linked to the teaching established in the previous verses—that believers are members of the body of Christ (verses 12–17). An immoral sexual union violates the believer’s mystical “one flesh” union with Jesus Christ (verse 15). We don’t have the right to use our bodies any way we wish because we belong to the Lord. Fornication runs contrary to our new nature and identity as members of Jesus Christ’s body. Paul goes on to explain that a Christian’s body is the temple of the Holy Spirit, a holy place that belongs to Jesus Christ (verse 19). We have been redeemed by God for good and righteous works and not for sin (Ephesians 2:10).
In both the Old and New Testaments, Scripture uses fornication in a figurative sense to describe the corruption of God’s people with the sin of idolatry and unfaithfulness. Both Israel and the church are depicted as the Lord’s wife, or the Bride of Christ. When God’s people engage in idolatry and unfaithfulness, He calls this sin “fornication” (Jeremiah 2:20–36; Ezekiel 16:15–43; Revelation 2:14, 20–22; 17:1–18; 18:2–9).