"You shall not steal" (Ex. 20:15). What does this commandment have to do with the boundaries between males and females? At first, it may not appear that this commandment has anything to do with such boundaries, but we shall see that this commandment is violated when these boundaries are crossed.
What are the boundaries between males and females? The apostle Paul wrote to the Corinthian Christians, "Now concerning the things about which you wrote, it is good for a man not to touch a woman" (1Cor. 7:1). We do not know what the Corinthians had written to Paul, but by the context of the chapter we can understand that Paul was addressing touching that provokes lust and leads to immorality (fornication). This is evident in the very next verse, for Paul wrote, "But because of immoralities, each man is to have his own wife, and each woman is to have her own husband" (1Cor. 7:2). In this, we see that the only godly alternative to men and women not touching one another is for each man to take a wife and each woman to take a husband. Of course, marriage is not mandatory for everyone, for Paul wrote, "But this I say by way of concession, not of command" (1Cor. 7:6). Indeed, marriage is not required for everyone, but it is the only permissible arrangement in which a man can touch a woman in a way that provokes passions. Paul's final word on this is this: "But if they do not have self-control, let them marry; for it is better to marry than to burn with passion" (1Cor. 7:9). In other words, if a man cannot control himself and simply must touch a woman, then let him marry her first.
Granted, not all touching between males and females is prohibited. Even our Lord touched a woman's hand to heal her (Matt. 8:15). Such chaste touching is permissible, but let us not abuse this to excuse behavior that clearly crosses the boundaries of what is acceptable. It is intellectually dishonest to pretend that there is no difference between a man and woman who shake hands versus a man and woman who handle each other in an unchaste way. We are not so naïve that we cannot understand the difference. However, if anyone cannot tell the difference or is provoked to lust by even a handshake, then let that person abstain from any touching whatsoever.
Let us be even clearer about these boundaries. Any touching that provokes lust in persons who are not married to one another violates the boundaries of godliness. Unbounded, lustful behavior is utterly unfitting for Christians, and it is expressly forbidden in Galatians 5:19-21. This passage lists "sensuality" or "lasciviousness" as a "work of the flesh" that will cause one to forfeit his inheritance in the kingdom of God. The definition of "sensuality" or "lasciviousness" (Gr. aselgeia, ἀσέλγεια) is unbridled lust, excess, wantonness, or shamelessness. This category of the works of the flesh certainly includes fornication and any form of sexual behavior or contact. It must also include what in days past was described as "heavy petting," which is lustfully using the hands to touch or stroke another person's body.
Does the act of kissing cross the proper boundaries between males and females? To find this answer, let us turn back to 1Corinthians 7:1-2. It is good for a man not to touch a woman because such touching arouses lusts and leads to immorality. The act of kissing certainly falls into this category. Granted, kissing does not always lead to immorality, but it does provoke the passions that are the motivation behind immorality. Consider that the first act of the adulterous woman in Proverbs 7:13 was to seize and kiss the young man she was seducing. Also notice that Paul did not set the boundary one step before fornication, but rather he set the boundary before the very first step down the path of fornication, which is touching. The Lord was even more restrictive, saying, "...everyone who looks at a woman with lust for her has already committed adultery with her in his heart" (Matt. 5:28). Because kissing exceeds the boundaries of both touching and looking, it is not proper behavior for unmarried people. Therefore, if a man wants to kiss a woman, then let him marry her first.
Going back to where we began, what does all of this have to do with stealing? The answer is this: When a man lustfully touches, kisses, or has sexual contact with a woman who is not his wife, he has taken something that does not belong to him. He has no right to these things. If he wants the right, then he must marry her. Merely intending to marry does not give him any rights to her, just as intending to buy a car would not give him the right to take the car from the dealership. Moreover, the fact that a woman is unmarried does not give a man any right to do such things with her. Even though she does not yet belong to any man as a wife, this does not mean that she is like "community property" and belongs to every man. Truly, no man has the right to contact an unmarried woman in these ways. In fact, it is just as wrong for a man to do these things with an unmarried woman as it is for him to do them with another man's wife. In both cases, he is taking something that is not his. Indeed, he is stealing.
It is expected that some will disagree with the ideas I have given here. They will find my words to be too restrictive. They may claim that they can touch and kiss other persons without arousing lust or behaving improperly. They may say that these are mere expressions of affection. I would ask them to be honest with themselves. Is there really no lust involved? Even if such a person is not provoked to lust, what about the other person? More importantly, what does the word of God teach? The ideas presented here are from the wisdom of Scripture and not from my opinions. It is not my interest to spoil anyone's "fun," but rather I seek to save souls, keep souls safe, and sound forth the will and wisdom of God.