Biblical Definition of Sexual Immorality: What Does the Bible Say?
The biblical definition of sexual immorality is any sexual activity that takes place outside the boundaries of marriage as defined by Scripture—specifically, a covenant union between one man and one woman139. This foundational truth shapes the Christian understanding of sexuality, purity, and God’s intent for human relationships.
Understanding the Term: What Does “Sexual Immorality” Mean in the Bible?
The New Testament uses the Greek word porneia to describe sexual immorality. Porneia is a broad term encompassing a variety of sexual sins, including but not limited to adultery, fornication (premarital sex), homosexuality, incest, bestiality, and prostitution139. The English word “pornography” is derived from this same root, highlighting the concept of “selling off” or surrendering sexual purity39.
“Sexual immorality is essentially the ‘selling off’ of sexual purity and involves sexual expression beyond the boundaries of a biblically defined marriage relationship.”39
The Foundation: God’s Design for Sex and Marriage
The Bible’s sexual ethic is rooted in the creation account. In Genesis 2:24, God establishes marriage as a covenant between a man and a woman:
“Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh.” (Genesis 2:24, ESV)
This “one flesh” union is the only context in which sexual intimacy is blessed and affirmed by God135. All other sexual activity is considered a distortion of God’s original design.
Key Biblical Passages on Sexual Immorality
Old Testament
Exodus 20:14: “You shall not commit adultery.”
Leviticus 18: Lists various prohibited sexual relationships, including incest, homosexuality, and bestiality.
New Testament
Matthew 19:4-6: Jesus reaffirms the Genesis model of marriage and sexual exclusivity.
1 Corinthians 6:9-10, 18: “Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality... will inherit the kingdom of God... Flee from sexual immorality.”
Galatians 5:19-21: Lists sexual immorality among the “works of the flesh.”
Ephesians 5:3: “But among you there must not be even a hint of sexual immorality, or of any kind of impurity, or of greed, because these are improper for God’s holy people.”
1 Thessalonians 4:3-5: “For this is the will of God, your sanctification: that you abstain from sexual immorality.”
What Behaviors Are Considered Sexual Immorality?
The Bible explicitly and implicitly includes the following under the category of sexual immorality:
Adultery: Sexual relations with someone other than one’s spouse7.
Homosexual acts: Sexual relations between people of the same sex (Leviticus 18:22; Romans 1:26-27)7.
Incest: Sexual relations between close relatives (Leviticus 18; 1 Corinthians 5:1)7.
Bestiality: Sexual relations with animals (Exodus 22:19)7.
Prostitution: Engaging in or soliciting sex for payment1.
Lustful thoughts: Jesus teaches that even lustful intent is a form of adultery in the heart (Matthew 5:27-28)7.
The Purpose of Sexual Purity
God’s commands regarding sexuality are not arbitrary. They are rooted in His character and His design for human flourishing2. The Bible teaches that sex is a sacred gift, meant to be enjoyed within marriage for:
Intimacy: Deepening the bond between husband and wife.
Procreation: Fulfilling God’s command to “be fruitful and multiply” (Genesis 1:28).
Reflection of Christ and the Church: Marriage is a living picture of Christ’s relationship with His people (Ephesians 5:31-32).
Any sexual activity outside this covenantal relationship is considered a misuse of God’s gift and is therefore sinful359.
Why Does Sexual Immorality Matter?
Sexual immorality is not just a private matter; it has spiritual, relational, and societal consequences. The Bible warns that persistent, unrepentant sexual sin can:
Separate us from God: “For of this you can be sure: No sexually immoral, impure or greedy person... has any inheritance in the kingdom of Christ and of God.” (Ephesians 5:5)6
Defile the body and soul: “Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body.” (1 Corinthians 6:18)
Harm others: Sexual sin often involves betrayal, exploitation, or injustice (1 Thessalonians 4:3-6)6.
Addressing Common Questions
Is Masturbation Sexual Immorality?
The Bible does not explicitly mention masturbation, but many Christian ethicists argue that it falls short of God’s design for sex, which is inherently relational and covenantal2. Masturbation is typically associated with lustful thoughts, which Jesus equates with adultery of the heart (Matthew 5:28)7.
What About Pornography?
Because pornography involves lust, objectification, and sexual expression outside of marriage, it is considered a form of sexual immorality139.
What If I’ve Already Failed?
The Bible offers hope and forgiveness for all who repent and trust in Christ. Sexual sin is not unforgivable. The apostle Paul writes to former sexual sinners, “And such were some of you. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.” (1 Corinthians 6:11)
Living a Life of Sexual Purity
God calls His people to holiness in every area, including sexuality. This means:
Fleeing sexual temptation (1 Corinthians 6:18)
Honoring God with your body (1 Corinthians 6:20)
Pursuing accountability and community
Renewing your mind with Scripture (Romans 12:2)
Trusting in the power of the Holy Spirit to transform desires and behaviors
Conclusion
The biblical definition of sexual immorality is clear: any sexual activity outside the marriage covenant between one man and one woman is sin in God’s eyes. This includes not only physical acts but also lustful thoughts and intentions. God’s design for sex is good, purposeful, and protective. While the world’s standards shift, the Word of God provides a firm foundation for understanding and living out sexual purity.
