The Bible’s Answer
The Bible’s answer to this question is yes. It is a sin to have sex—or any kind of sexual relation—with anyone other than your spouse. The author of the letter to the Hebrews wrote: “Let marriage be held in honour among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous” (Hebrews 13:4, ESVUK). The Apostle Paul wrote about how to keep the “marriage bed undefiled” in his first letter to the Corinthians. He wrote:
Now concerning the matters about which you wrote: “It is good for a man not to have sexual relations with a woman.” But because of the temptation to sexual immorality, each man should have his own wife and each woman her own husband. The husband should give to his wife her conjugal [sexual] rights, and likewise the wife to her husband. … Do not deprive one another, except perhaps by agreement for a limited time, that you may devote yourselves to prayer; but then come together again, so that Satan may not tempt you because of your lack of self-control. (1 Corinthians 7:1–3, 5)
Paul further wrote: “if they [the unmarried and widows] cannot exercise self-control, they should marry. For it is better to marry than to burn with passion” (1 Corinthians 7:9). Marriage, therefore, is a blessing and gift of God for people who have strong sexual desires. In the life-long bond of marriage, God permits two people—male and female1—to have sex together. Therefore, having sex before you are married, or with anyone other than your spouse, defiles the marriage bed, and is the sin of fornication/adultery. Paul warned that unless the “sexually immoral” and “adulterers” (among others) repent of such sins, they will not inherit the kingdom of God (1 Corinthians 6:9–10).
The Sanctity of Sex and Marriage
Many people nowadays treat marriage as a mere legal contract issued by the government, rather than what it really is: the sacred, life-long covenantal union between one man and one woman, instituted by God. The Word of God says: “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). Our Lord Jesus Christ, who is the God of the Old Testament (cf. Genesis 1:1–2 with John 1:1–3), echoed these words in the New Testament. He declared:
Have you not read that he who created them from the beginning made them male and female, and said, ‘Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh’? So they are no longer two but one flesh. What therefore God has joined together, let not man separate. (Matthew 19:4–6)
As we can see, God was the one who instituted marriage, not human beings. Therefore, we must uphold and honour marriage on God’s terms, not our own. Because one of the purposes of marriage (as discussed above) is to allow sex to be done in a non-sinful context, sex outside of marriage is a direct attack against God’s purposes for human sexual relations. Adultery is such a serious sin that, under the old covenant (which we are no longer under, see Hebrews 8:13), any person in the land of Israel who committed adultery with another man’s wife would be put to death—both the adulterer and adulteress (Leviticus 20:10).
Lust Is a Sin
Many people assume that the New Testament is less strict than the Old Testament for various reasons. In some instances, however, Jesus actually heightened the moral standards of the Old Testament law. For instance, according to Jesus, it is not simply a sin to commit the physical act of adultery, but to even look at a woman (or man) who is not your spouse with lustful intent:
You have heard that it was said, ‘You shall not commit adultery.’ But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart. (Matthew 5:27–28)
Now, of course having lustful thoughts is not as bad as going to a person and physically committing adultery with them. Our Lord does distinguish between greater and lesser sins (Matthew 10:14–15; John 19:11). However, lustful thoughts are still sinful, and Jesus wants us to keep our minds pure, not simply our words and deeds (Philippians 4:8). After all, what proceeds from the mouth, comes from the heart; if a person is filled with evil thoughts inside, then unless they control them, such thoughts will manifest in their actions (Matthew 12:34–35). Solomon wisely warned: “He who commits adultery lacks sense; he who does it destroys himself” (Proverbs 6:32).
Consider Other People’s Feelings and Lives
Sex outside of marriage is an inherently selfish activity, because to do it, you must disregard the interests, feelings, and lives of others. For example, think of how heartbroken your husband or wife would be if you slept with another person. That could destroy your marriage. Or, think of how hurt or awkward your future spouse would feel if you told them that you have already had sex with another person before, outside of marriage. They may have difficulties in trusting your faithfulness, as a result.
The most important question, though, is if contraception2 was not used—or fails—how would sex outside of marriage affect the child? Will the child grow up with only a single mother? Will the child be given up for adoption or foster care, and grow up without knowing his or her biological parents? Or, worst of all, will the baby be murdered through abortion or the morning-after pill before he or she can even be born? Exodus 21:22–25 shows us that God considers unborn babies equal to fully-grown adults. It seems that most people who have sex outside of marriage would not consider any of the above—they are merely interested in pleasure. This is not how Jesus and Paul taught us to live, though:
So whatever you wish that others would do to you, do also to them, for this is the Law and the Prophets. — Jesus Christ (Matthew 7:12)
Do nothing from rivalry or conceit, but in humility count others more significant than yourselves. Let each of you look not only to his own interests, but also to the interests of others. — Paul the Apostle (Philippians 2:3–4)
Additional Consequences of Sex Outside of Marriage
Paul gives all people—especially Christians—another strong incentive for not having sexual relations with people outside of marriage. In his first letter to the Corinthians, he wrote:
Do you not know that your bodies are members of Christ? Shall I then take the members of Christ and make them members of a prostitute? Never! Or do you not know that he who is joined to a prostitute becomes one body with her? For, as it is written, “The two will become one flesh.” But he who is joined to the Lord becomes one spirit with him. Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body. Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body. (1 Corinthians 6:15–20)
Indeed, through baptism and faith (Romans 6:3–5), we become one spirit with Christ and temples of the Holy Spirit. If a Christian has sex with a prostitute (or anyone other than their spouse), their bodies become spiritually one, and thus the holy temple of God is profaned by a forbidden union, rather than the godly union of marriage. This is why we should honour God in our bodies, because by keeping our bodies pure, we are keeping that which God dwells in and has redeemed pure. For non-Christians, by having sex outside of marriage, they also sin against their own bodies—and thus profane what God has created (Psalm 139:13–14; Genesis 1:26–27).
The Bible teaches that to have sex with anyone other than your spouse is the sin of adultery. Marriage is a blessing of God, in which one man and one woman, united by God in a life-long covenant, may have sex with each other. Adultery was punishable by death under the old covenant, and the new covenant warns that people who do not repent of it will go to Hell. Marriage was instituted by God, not humans, and so we must uphold it on God’s terms, not our own.
Even lustful thoughts, which plant the seeds of physical adultery, are sinful according to Jesus. Having sex outside of marriage is an inherently selfish activity, which prioritises personal pleasure over the lives, feelings, and interests of others. Finally, having sex with anyone other than your spouse is a sin against your own body—a creation of God, and Christians who do this profane the Holy Spirit’s temple.
If you have ever had sex outside of marriage or dwelt on lustful thoughts, are genuinely sorry for it, and desire forgiveness from God, then please read the article below.
- Many countries have recently legalised “same-sex marriage“, i.e., allowing two persons of the same sex to marry one another. According to the Bible, though, marriage is only between one man and one woman, so same-sex (or homosexual) marriages are not real marriages, and are thus adulterous relationships (Matthew 19:4–6). Furthermore, the Bible teaches that homosexuality (same-sex attraction) is a sin that should be rejected at all costs (Romans 1:26–27; 1 Corinthians 6:9–10; Leviticus 20:13).
- Beware: some medical “contraception” actually act as abortions, which terminate the development of the already-fertilised egg in the uterus—thus ending the first stage of human life. Such forms of contraception are clearly immoral and should never be used.