Question: "What does the Bible say about sex before marriage / premarital sex?"
Answer: Along with all other kinds of sexual immorality, sex before marriage / premarital sex is repeatedly condemned in Scripture (Acts 15:20; Romans 1:29; 1 Corinthians 5:1; 6:13,18; 7:2; 10:8; 2 Corinthians 12:21; Galatians 5:19; Ephesians 5:3; Colossians 3:5; 1 Thessalonians 4:3; Jude 7). The Bible promotes 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 you are not married to. Sex between a husband and his wife is the only form of sexual relations that God approves of (Hebrews 13:4).
Sex before marriage has become so common for many reasons. 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. 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.