Many people have told me that fornication means sex before marriage. Is this the correct definition? What scripture defines it as such? Is this sin worse than any other?
Fornication comes from a Greek word whose meaning includes: pre-marital sex, adultery, incest, homosexuality/lesbianism, and bestiality. So, fornication includes sex before and after marriage. There are scripture references that prohibit all of these sins.
Fornication does appear to have a worse impact on us than most other sins. I have found this to be true in counseling couples. This sin is often present with couples who are struggling in their marriage. Listen to 1 Cor. 6:18
Flee immorality. Every other sin that a man commits is outside the body, but the immoral man sins against his own body. (NASB) 1 Corinthians 6:18
This is the only sin committed against the body and its impact is significant. It is often the wife who is angry and resentful. It is interesting that recent psychological studies are showing that couples who have had premarital relations are having a higher rate of divorce than couples who avoid premarital sex. Premarital sex is not a test of compatibility but a time bomb that destroys marriage. God knows how He made us. He has warned us.