From Christian Q&A site GotQuestions.org:

The Bible nowhere directly and explicitly states that sex before marriage is a sin. The Bible undeniably condemns adultery and sexual immorality, but the question arises, is sex before marriage considered sexually immoral?

According to 1 Corinthians 7:2, “yes” is the clear answer, “But since there is so much immorality, each man should have his own wife, and each woman her own husband.” In this verse, Paul states that marriage is the “cure” for immorality. If sex before marriage is not immoral, this verse would not make any sense. 1 Corinthians 7:2 is essentially saying, “because so many people are having immoral sex outside of marriage, people should get married.”

So, on the basis of 1 Corinthians 7:2 clearly including sex before marriage in the definition of sexual immorality, all the Bible verses that condemn sexual immorality as being sinful also condemn sex before marriage as sinful. Sex before marriage is included in the definition of sexual immorality. Therefore, there are countless Scriptures that condemn sex before marriage (Acts 15:20; 1 Corinthians 5:1; 6:13,18; 10:8; 2 Corinthians 12:21; Galatians 5:19; Ephesians 5:3; Colossians 3:5; 1 Thessalonians 4:3; Jude 7).

The Bible promotes complete abstinence before marriage. Sex before marriage is just as wrong as adultery and other forms of sexual immorality, because they all involve having sex with someone other than your spouse. The biblical definition of sexual immorality is sex outside of marriage. Sex between a husband and his wife is the only form of sexual relations of which God approves (Hebrews 13:4).

Far too often we focus on the “recreation” aspect of sex without recognizing the “re-creation” aspect. Yes, sex is pleasurable. God designed it that way, and He wants men and women to enjoy sexual activity (within the confines of marriage). However, the primary purpose of sex is not pleasure, but rather reproduction.

God does not outlaw sex before marriage to rob us of pleasure, but to protect us from unwanted pregnancies and children born to parents who do not want them or are not prepared for them. Imagine how much better our world would be if God’s pattern for sex was followed: fewer sexually transmitted diseases, fewer un-wed mothers, fewer unwanted pregnancies, fewer abortions, etc.

Abstinence is God’s only policy when it comes to sex before marriage. Abstinence saves lives, protects babies, gives sexual relations the proper value, and most importantly, honors God.


Recommended Resource: Why True Love Waits by Josh McDowell.
Men - Every Young Man's Battle : Strategies for Victory in the Real World of Sexual Temptation by Stephen Arterburn.
Women - Every Young Woman's Battle: Guarding Your Mind, Heart, and Body in a Sex-Saturated World by Shannon Ethridge.