When one wants to divorce their spouse in order to marry someone else, but they can’t find scriptural justification for their action, they will either try to dismiss the restriction by saying the command is not relevant today, or they will try to widen the restriction so that what they want is included in the commandment. In other words, they want to change God’s word to fit their life, opposed to changing their life to fit God’s Word.
Fornication refers to illicit sexual acts that take place outside of the bonds of marriage, including adultery, homosexual acts, incest, oral sex, etc. However, does fornication include sexual lusts of the mind? Jesus stated, “But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart” (Mt 5:28). In this statement, Jesus is not saying that sexual lust is adultery, but that it is equivalent to adultery. In other words, sexual lust for someone who is not your spouse is just as much a sin as actually committing the act of adultery. Jesus is not stating that they are the same sin. The point that Jesus is attempting us to learn is that desiring to commit a sin and actually committing the sin is not that different to God. The Jews emphasized the physical to the point that they excused or dismissed the spiritual implications of the law. They knew that adultery was wrong, but thought there was nothing wrong with thinking about it just as long as a person didn’t actually do it. Jesus is pointing out that sins originate in the heart (Mk 7:21-23). The only difference between thinking about sin and committing sin is the opportunity to act on your thoughts.
The point is that sexual lust and acts of sexual immorality are equally wrong. Lust is not a lesser sin than adultery as the Jews had been debating. John makes a similar argument between hatred and murder. “Whoever hates his brother is a murderer, and you know that no murderer has eternal life abiding in him” (I Jn 3:15). However, this does not mean that when you hated your parents for not letting do something that you had murdered them. John’s point is that hatred is not a lesser sin than murder. Both are equally wrong. The difference between the two is the opportunity for action. As one lawyer pointed out in a court of law concerning the difference between imagining to rob a bank and actually robbing it, is about 30 years.
In Mt 19:9, Jesus is referring to the acts of fornication, not just the thoughts of fornication. Several difficulties would arise if thoughts were included, but the most difficult would be proof. “For what man knows the things of a man except the spirit of the man which is in him?” (I Cor 2:10). Could a wife demand a divorce because her husband looked at pornography, watched a movie that included scenes of fornication, or looked at a woman walking down the street too long? If so, then no marriage would be safe from divorce. In fact, all are guilty of looking at pornography. I comes in books, magazines, art, and the internet. You may try to avoid it, but to do so, you would need to leave this present world. This mind of man is a very wicked thing that he must learn to obtain eternal life. If a wife was convinced that her husband was thinking about other women, even though she had no evidence of it, could she demand a divorce and then remarry? Surely not!
Lusting after a woman who is not your wife is sinful. It could keep you out of heaven if not repented of. However, fornication in Matthew 19:9 refers to act of fornication and not the thoughts of fornication.
If a woman decided to divorce her husband because of his involvement in pornography (and she really should not do so), she would have to remain unmarried for the rest of her life. “Now to the married I command, yet not I but the Lord: A wife is not to depart from (divorce) her husband. But even if she does depart (divorce), let her remain unmarried or be reconciled to her husband. And a husband is not to divorce his wife” (I Cor 7:10-11). In the whole scheme of life, the only men or women who are even using this argument are the ones trying to escape the bonds of marriage. Most everyone is guilty of this sin at one time or the other in their life. It’s a sin that needs to be stopped, repented of, and never done again. As Job said, “I have made a covenant with my eyes; Why then should I think about a young woman.” (Job 31:1) Is looking at pornography grounds for divorce? Only when in reference to your soul. Yes, God will divorce you is you don’t repent of this sin. However, it is not grounds for divorce from your spouse. That requires both the thought and action of fornication.