Why is sex before marriage wrong?

Short answer: because Jesus says so.

A student asked me this question last year, and that was the answer I gave him. I told him and the others in the discussion that in Mark 7:21, Jesus lists serious sins, "murder, adultery, theft, fornication (sex outside of marriage)". While he showed respect for our Lord's teaching, he went on to argue for fornication. Sometime later, he passionately summed up his position: "I just don't think there's anything wrong with sex outside of marriage". I replied, "so, you disagree with Jesus".

Just about every young Catholic who has ever asked me this question does not know Mark 7:21. They do not know that Jesus has said that sex before marriage is wrong. Once they find out that God has condemned fornication, they still want to know why it's wrong. In other words, they now get THAT sex before marriage is wrong, but still don't get WHY it's wrong.

Sex before marriage is wrong because it involves lust, not love. You're thinking, 'how can you say that, Father?' Granted, when I'm speaking to unmarried people who are involved in a sexual relationship (the time when people most disagree with the Church's teaching), I gently and slowly make this point clear. They usually realize it before I have to spell it out. I can say it because it's true. I am speaking about the act itself, not the couple. The couple can truly love each other, but still commit sins of lust. Even married couples can commit sins of lust against one another (e.g., oral sex).

Any sexual act* outside of marriage is a sin of lust. A sin of lust occurs when you use another for your own sexual pleasure. You reduce them to being merely an object of your sexual desire. We can contrast lust with love by saying simply that lust means taking from another while love means giving to another. When the unmarried couple engages in sex, they enter into lust, not love. How? Because they are taking from the other, not giving. They CANNOT give themselves to the other. An unmarried couple has not given their love to each other in marriage, so they are incapable of fully giving their love to each other physically. This is a HUGE point in understanding why sex outside of marriage is wrong and bears repeating. An unmarried couple has not given their love to each other in marriage, so they are incapable of fully giving their love to each other physically. If it's not love, it's lust.

"But, Father, I really love my boyfriend. It's not about sex, it's about making love". Where do we get the idea of "making love", anyway? Is it from movies and TV? If Hollywood is the authority on love, then yes, you and your boyfriend of four weeks truly love each other and express that love every time you exchange the most intimate human act of sex. But, Hollywood is not the authority on love- God is. He is the author of love! "God is love" (1 Jn 4:8). And, the author of love has written (in the first book of the Bible, Genesis) that sex is for two purposes: procreation and union (between husband and wife). An unmarried couple can't truly unite, so they can't "make love", as God intends. God intends them to be married and to be open to life when they have sex! Engaging in sex as God intends is truly making love. Then, sex is sacred, holy, beautiful, pure, and good. Outside of that, sex is evil, as Jesus says in Mark 7:21.

*to see what constitutes a sexual act, check out my upcoming post, “How far is too far?”