Answer:

Let's start with what most people would agree would be going too far: sexual intercourse or fornication. Sexual acts outside of marriage are sinful and are covered under the word "fornication." In Greek, the word is porneia. It is from this word we get our word "pornography," which literally means acts of fornication depicted in a visual or written way. Many new translations use the more vague phrase "sexual immorality" or sometimes just "immorality" to translate porneia because they believe "fornication" is an outdated word that people won't understand. As Glendol McClure notes, "The term 'fornication' generally refers to unlawful sexual intercourse between the unmarried, but the term is also applied to include illicit sexual intercourse between two people who are married. The term fornication would include incest, prostitution, lesbianism, homosexuality, bestiality, pedophilia, and adultery" [Living in Adultery]. Thus when Paul states, "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God" (I Corinthians 6:9-10). The word "fornication" becomes the catch-all for all other types of sexual sins which are not more specifically stated in the other terms.

Many people want to know exactly where the boundaries are. Exactly what constitutes fornication? Does it include anal sex or oral sex? "Sex" is defined to be those actions that generally lead to orgasm, and for males the release of semen. It does not have to be restricted to a man's penis entering a woman's vagina. Oral sex and anal sex are still acts of sex, and they still include the penis going into another person. This is how sex was literally described in the Bible: "He went in to Hagar, and she conceived" (Genesis 16:4). By this definition of sex, mutual masturbation (commonly called "hand jobs") would also be included.

If we stopped there, people would conclude that as long as you didn't commit the act of sex, anything less than that would be acceptable. That is what the Jews in Jesus' day had concluded. They emphasized the wrongness of the actual act, but ignored what leads up to that act. Jesus pointed out the fallacy of their position: "You have heard that it was said to those of old, 'You shall not commit adultery.' But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart" (Matthew 5:27-28). Sin doesn't start when you actually do something wrong, it also includes contemplating sin, such as looking at a woman and wondering what she would be like in bed. "What comes out of a man, that defiles a man. For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, thefts, covetousness, wickedness, deceit, lewdness, an evil eye, blasphemy, pride, foolishness. All these evil things come from within and defile a man" (Mark 7:20-23).

Paul makes a very similar argument: "For this is the will of God, your sanctification; that is, that you abstain from sexual immorality; that each of you know how to possess his own vessel in sanctification and honor, not in lustful passion, like the Gentiles who do not know God" (I Thessalonians 4:3-5). God wants people to be set apart as something special and dedicated to God. When people are involved in fornication, they are no longer sanctified. They now are just like the rest of the world, given over to sin. They are not special, they are common. But what God wants are people who know how to practice self-control. They don't let their physical desires control their decisions. But if fornication is wrong, then the things that lead up to a loss of self-control and fornication are just as wrong. Thus, passionate things that arouse the desire for sex outside of marriage are also wrong. This would definitely include pornography, but what about couples sending naked pictures of themselves? They may argue that there is no harm because they are not in the same place, but it still raises the desire for fornication and can lead to a loss of self-control.

A similar passage is: "But immorality or any impurity or greed must not even be named among you, as is proper among saints; and there must be no filthiness and silly talk, or coarse jesting, which are not fitting, but rather giving of thanks. For this you know with certainty, that no immoral or impure person or covetous man, who is an idolater, has an inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience. Therefore do not be partakers with them" (Ephesians 5:3-7). "Filthiness" is what is commonly called "dirty talk." It is sexually charged talk; thus, it isn't just visual eroticism that would be wrong, but anything that gives another person the impression that you might think fornication is acceptable. When Paul talks about "any impurity", he is referring to a state of mind that is the opposite of holiness. "For God has not called us for the purpose of impurity, but in sanctification" (I Thessalonians 4:7). Sometimes we refer to someone as having a "dirty mind" and that is impurity. However, it can also include impure action, such as removing clothing in front of your girlfriend. Such actions signal a desire for sexual stimulation that is not proper.

Since fornication is wrong, attempting to stimulate a desire for sex is also wrong. "Now concerning the things about which you wrote, it is good for a man not to touch a woman" (I Corinthians 7:1). Some modern translations completely miss the point that Paul is making and translate it as "it is good for a man not to marry a woman," which is a contradiction of other passages, such as Paul's later statement in I Corinthians 7:28. What Paul is talking about is not sexually touching a woman you are not married to. Since it is wrong to have sex outside of marriage, you don't touch another person to arouse the desire for sex. Once you do so, you cannot claim innocence when events go further than you intended and you end up engaging in sex. "So is the one who goes in to his neighbor's wife; whoever touches her will not go unpunished" (Proverbs 6:29).

This would also include passionate kissing and touching where the couple loses themselves in sexual feelings. "Lewdness" or "sensuality" refers to shameless behavior, particularly in regard to sex. It is behavior that is involved in pure self-enjoyment or behavior characteristic of an animal. "Let us behave properly as in the day, not in carousing and drunkenness, not in sexual promiscuity and sensuality, not in strife and jealousy. But put on the Lord Jesus Christ, and make no provision for the flesh in regard to its lusts" (Romans 13:13-14).

To put this all in more simple terms, sin doesn't begin when fornication takes place. Fornication is the destination, and it lies on a path filled with other sins. If you don't want to reach the destination, then you have to stay off the path. "Do not enter the path of the wicked and do not proceed in the way of evil men. Avoid it, do not pass by it; turn away from it and pass on" (Proverbs 4:14-15). Instead of looking for the border and wondering how close you can get to them by crossing over, head in the opposite direction.

There is nothing wrong with holding hands with your girlfriend or giving her a brief good night kiss when you drop her off at her doorstep, but anything generated by your desire for sex should be avoided.