Your Question: Where does the Bible teach it is wrong to have sex before marriage?
God is the inventor of marriage. When God created Eve, Adam was very happy. They clearly belonged together. The conclusion is: “Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh” (Genesis 1:24). ‘One flesh’ refers to sexual unity, but also to the deeper spiritual unity between husband and wife in marriage. These two things go together. Sex is for marriage and marriage is for sex.
Sex is part of God’s wonderful creation, and it is to be enjoyed in the way God designed it: within the bonds of marriage. The first chapter of the Bible already makes this clear.
In the rest of the Bible God’s design –sex is to be enjoyed in marriage- is always assumed. This is especially clear from the fine that a man has to pay for sleeping with an unmarried virgin (Exodus 22:16-17) and from the requirement that a woman should be a virgin on her wedding night (Deuteronomy 22:13-21).
The New Testament also clearly teaches that sex before marriage is a sin. In Mark 7:20 Jesus gives a list of sins. Among them are ‘sexual immorality’ and ‘adultery’. So there is sexual immorality that is not adultery. Sexual immorality refers, among other things, to sex before marriage. Paul says the same in 1 Corinthians 7:2: “Because of the temptation to sexual immorality, each man should have his own wife and each woman her own husband.” So if you want to have sex, there is only one way not to fall into sexual immorality: to have your own husband or wife.
However, the Bible has a positive view of sex within marriage. Song of Songs speaks positively of the longing of a man and a woman for each other. Sex is not to be hidden because it is dirty, but it is to be protected because it is precious. Marriage is the protection that God has given us for this precious gift.
Hebrews 13:4 encourages us “let marriage be held in honor among all, and let the marriage bed be undefiled.” Following God’s rules rather than our own desires is the best guarantee for our long term happiness, also in the area of our sexuality.