This question used to have an obvious answer back in the days when our parents were young. "God says so!" But when studying Scripture and looking for a firm, definitive answer, it is quite possible for a Believer to miss God's answer. Why is this? We shall see in just a few moments.
God's answer to this question primarily lies in the Old Testament. We have heard it said many times, "That is the Old Covenant--that doesn't apply anymore" or "The Old Testament is no longer the way." This is a very dangerous way to look at the ancient text.
And this lesson will exactly be teaching, rebuking, correcting, and training in righteousness from all of Scripture for the glory of Christ. We truly have a gracious, patience, and loving God who works with us to rid our lives of sin.
Let's quickly dive into the Scriptures to see what God says about this. As inferred before, there is no commandment like "thou shalt not have sex before marriage" or "it is a sin to have sex before marriage". The main reason for this was the fact that marriage and sex went hand in hand. In fact, in Israel it was law that if a man had sex with a woman, even if he rapes her (Duet 22:28:29), he MUST marry her. God says that two will become one flesh. It is sex that is the act of becoming one flesh.
Shechem and Dinah
Although we may not find one verse that tells us right from wrong regarding this subject, there are several Old Testament stories that do. First--and the strongest--is the story of Dinah and Shechem in Genesis 34. Dinah was a virgin daughter of Jacob, and Shechem was a Hivite ruler (non-Jew) who liked Dinah. Genesis 34:2 says that he took her and violated her. This is not rape; Shechem stripped her of her virginity before marriage. We will see in Deut 22 how important virginity is for women in marriage.
The reason this is not rape is for the following reasons.
Also, Dinah was not at her home; she was in Shechem's home city (Gen 34:27), which implies some sort of consent to being with him. Genesis 34:3 says that Shechem loved her and spoke tenderly of her. There was a relationship here.
Since Shechem liked Dinah and was a non-Jew ruler, he worked with his father to receive her hand in marriage. So we see that this certainly was pre-marital sex--they were not married yet when he violated her. Genesis 34:7 shows how horrible these events were:
Genesis 34:7. Now Jacob's sons had come in from the fields as soon as they heard what had happened. They were filled with grief and fury, because Shechem had done a disgraceful thing in Israel--a thing that should not be done.
The story continues and ends after two of Jacob's sons kill all of the males in the city, particularly Shechem, his father and brothers. Dinah is, however, rescued and not punished. Needless to say, this issue was serious enough to get many men killed.
Jacob and Rachel
This is not "good enough" to convince many because an argument, although weak it would be, can be made that this was rape and not consensual sex. Well, we can back up a few chapters and see that waiting to have sex until being married is the right thing to do. Genesis 29 starting in verse 15 tells a story how Jacob worked for seven years to marry his wife. Laban was the father of a beautiful daughter, Rachel, and Jacob loved her very much (Gen 29:18-20). Jacob proposed to her father that he would work for him for seven long years for the rights to marry. It was agreed, and after the seven years, Jacob said a very interesting thing to Laban in verse 21: "Give me my wife. My time is completed, and I want to lie with her." Jacob had "dated" Rachel for SEVEN YEARS without having sex with her. Doing so would have violated her and her father. By waiting to have sex until after marriage, Jacob did what was right!
God's Laws
As we mentioned before, a woman's virginity is very important when getting married. This is described in extreme detail in Deut 22:13-21, which is part of the law in Israel given by God. Yes, we are not in Israel nor are we bound by the law, but this was what God saw as best for his people, so we can be taught and rebuked with this passage. The passage talks about a man getting married and then claiming that his new wife was not a virgin. If the parents of the girl could prove her virginity (which was possible!), then the man would be severely punished.
But if indeed the man had married a girl who was thought to be a virgin but was not, then Deut 22:21 has a something convicting to say: "she shall be brought to the door of her father's house and there the men of her town shall stone her to death. She has done a disgraceful thing in Israel by being promiscuous while still in her father's house. You must purge the evil from among you." Did you catch the tone of this statement? The girl, who obviously had pre-marital sex, was described as evil, promiscuous, and disgraceful. She was put to death. Praise Jesus for taking this punishment for us who are guilty of this sin! His Grace is sufficient.
Another bit of law that directly ties to pre-marital sex is a couple verses latter in 23 and following. If a virgin girl is pledged to be married (which obviously means that she is not married yet) and has consensual sex with another man, they were both to be executed. The man was executed for violating the girl (notice that violating in this verse is not rape, just like Genesis 34:2), and the girl was executed for consenting to the sex. "You must purge the evil from among you." This was evil in Israel, but it is sad to know that in the world today, this is okay and even many times glorified. God must certainly be very hurt by this. He has definitely been patient with us.
Boaz and Ruth
Another story of how waiting was the good thing to do is the story of Ruth. This is a fantastic story of love, faithfulness, and submission. I will only summarize here, so I strongly suggest that you read the story soon after receiving this lesson. Ruth was a non-Jew and a widow who left her homeland to be with the Jews; basically, she was a foreigner who had already been married. She was not exactly the most attractive girl socially, although she was beautiful spiritually and physically. She worked hard in Israel and gained respect. An innocent relationship began between her and Boaz, an older gentleman who was unmarried. To understand what happens next, we must understand a Jewish custom. A widow would give a sign that she would consent to marrying a relative of her husband. This sign would be to sleep at the man's feet on the floor. Well, as it is written in Ruth chapter 3, she did exactly this one night after working hard in the fields. Boaz fell asleep on the threshing floor, and Ruth approached quietly and slept at his feet without him knowing this. He woke up in the night, and was shocked to find Ruth at his feet! He told her that she showed him great kindness because she did not run after the younger and more eligible bachelors. He knew that Ruth was of noble character. He then told her to continue sleeping, and he covered her with a garment. They did not have any sex. Then the next day, Boaz had one thing in mind--to go through the necessary requirements to marry Ruth. He married her, and it is said in Ruth 4:15 that she was better than seven sons! How amazing! And what is more amazing than this is that Ruth is directly in the ancestry of Jesus the Christ our Savior. Her noble character brought her glory.
Sodom and Gomorrah
Another story to look at briefly is Sodom and Gomorrah. It is safe to say that the people of Sodom and Gomorrah were sexually immoral. God destroyed them completely for it. Although there is no mention of pre-marital sex in Sodom, I believe it was commonly accepted there by looking at the Scriptures in Genesis 19. Lot (who had many moral problems himself) was hosting two angels at his house when the men of Sodom--young and old--came to Lot's house. They demanded that the angels come out of the house so they could have sex with them! How despicable! Then Lot shocks us by responding to these men in verse 8: "Look, I have two daughters who have never slept with a man. Let me bring them out to you, and you can do what you like with them. But don't do anything to these men." Amazing that Lot would allow this, but obviously Lot believed that maybe the men would rather enjoy having orgies with virgin girls than with angels. Reading this, do you believe that pre-marital sex was considered acceptable in this society of Sodom? And if so, do you think God thought that it was acceptable to Him (remember that He destroyed Sodom)?
Jesus' Teachings
We can wrap all this up in the New Testament. Jesus described adultery in the Sermon on the Mount. Matthew 5:27-30 describes adultery to its fullest. Jesus said, "I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart." This does not particularly single out pre-marital sex in any way, but if this is what Jesus said about just looking and not touching, what do you think Jesus would say about pre-marital sex? And notice that Jesus said anyone, not just married men. This is all men, married and unmarried. So if Jesus said that an unmarried man looking lustfully upon a woman has committed adultery in his heart, would it not be safe to say that a unmarried man who has sex with a woman has committed adultery?
Adultery can be easily defined as having any sexual tendency with someone who is not your spouse. This is a very conservative view that says that pornography is wrong, masturbation is wrong, affairs are wrong, and pre-marital sex is wrong. Sex is to be between husband and wife. That is all.
Paul's Teachings
There is a very interesting passage in 1 Corinthians about men and women getting married. Paul says to the Corinthians, "Now to the unmarried and the widows I say: It is good for them to stay unmarried, as I am. But if they cannot control themselves, they should marry, for it is better to marry than to burn with passion. (1 Cor 7:8-9)" This passage is a clear indication that unmarried people who cannot control their sexual desires should get married because that is better than having that burning, unsatisfied desire. This may not say that pre-marital sex is a sin, but it certainly says that getting married is better than having those pre-marital sexual desires.
Finally, we mentioned earlier that two become one flesh. The act of sex unites a male to the female. This is undeniable with proof from 1 Corinthians 6:16: "Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, 'The two will become one flesh.'" This is a warning against becoming one with the wrong person and the wrong god. We run a great risk of uniting with the wrong person with pre-marital sex. Paul echoes Jesus' consequences to this type of sin (Matt 5:29-30) in the following passage.
1 Corithians 6:18-20. Flee from sexual immorality. All other sins a man commits are outside his body, but he who sins sexually sins against his own body. Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? You are not your own; you were bought at a price. Therefore, honor God with your body.
Repentance and Grace
Our God is an awesome God. He is Just and Holy. He does expect righteousness that comes from faith. Though we sin against Him and our bodies, He is still willing to pour out His Grace! He gave us Christ for this purpose, and we can continue to nail our sins to the cross. "God opposes the proud but gives grace to the humble." Let us be humble by recognizing that our sexual sins are deserving of death, but Jesus Christ took that for us. That is Grace. In John 8:11 Jesus said, "Then neither do I condemn you. Go now and leave your life of sin."