"You have heard that it was said, 'You shall not commit adultery.' But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart" (vv. 27–28).
Christ's exposition of the seventh commandment in Matthew 5:27–30 indicates how the biblical teaching on adultery goes contrary to much of what our society wants to tell us about sex. Most people, at least in our culture, are unlikely to have consummated an extramarital affair. Single people are not even capable of committing adultery in the narrow sense of an affair unless they are sleeping with a married person. However, few, if any, could ever say that they have never looked at another person with lust in their hearts. We live in a pornographic society that relishes and encourages all manner of illicit sexual activity.
In demonstrating that the seventh commandment was given also to prohibit lust, Jesus is not somehow saying that an unconsummated lustful intent is sinful to the same degree as an actual extramarital affair (though both sins merit punishment). The latter is a more blatant violation of the statute against adultery, and it has greater consequences in the form of divorce and the loss of one's reputation as a trustworthy person. Nevertheless, all extramarital affairs start in the heart with lustful desires that are nurtured and indulged instead of fought through repentance and resistance. From James 1:12–15, as well as human history and experience, we may rightly infer that lust is the first step toward sexual sin, and it falls under the scope of transgressions forbidden by the seventh commandment.
Of course, we must actually know what lust is if we are to resist it. Lust is not sexual desire in and of itself, for sexual desire is part of God's good creation and the consummation of it is entirely lawful within marriage (Gen. 2:23–24). Moreover, lust is not the mere recognition of physical attractiveness. The Lord made us to recognize beauty, and Scripture itself speaks, without breaking God's law, of the beauty and handsomeness of some of the people it describes (Gen. 29:17; 1 Sam. 16:12; 25:3). Instead, lust may be defined as the desire to engage in or enjoy illicit sexual activity. Given this definition, a whole host of things qualify as lust, including the viewing of pornography, adulterous fantasies, homosexual behavior, incest, sexual abuse, rape, bestiality, and other perversions. In prohibiting lust, our Creator prohibits all of these things.
Coram Deo
Positively, question and answer 109 of the Heidelberg Catechism note, the seventh commandment encourages the maintenance and promotion of chastity in marriage and singleness. We should be doing all that we can to prevent a climate in the church and in our homes that may make adultery easy to commit and hide. We must also regularly return to the Bible’s teaching on sexuality so that we can resist the lies about lust and sex that our culture loves to tell us every day.
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