Note that the antitheses found in the Sermon on the Mount do not say that all sins are equal in degree. For example, ungodly anger and the act of murder both violate the intent of Exodus 20:13 (Matt. 5:21–22), but the hot-head and the murderer do not get the same punishment (Num. 35:9–29). Both sins make men guilty before our Creator and bring eternal death if there is no repentance (Rom. 3:23). Nevertheless, God punishes sinners in hell in proportion to the gravity of their sin and what has been revealed to them (Matt. 11:20–24).
Furthermore, Christ’s teaching on anger also shows us that we must not only refrain from forbidden acts, we must do all we can to encourage their opposite. It is not enough to keep from being angry unjustly with a Christian brother or sister; we must do all we can to ensure that they have no cause to be angry with us. We must pursue reconciliation and loving relationships as far as we are able (5:23–26). Thus we can see why the Westminster Larger Catechism says that “where a duty is commanded, the contrary sin is forbidden; and, where a sin is forbidden, the contrary duty is commanded” (Q. 99).
According to this principle, a thorough exegesis (interpretation) of today’s passage tells us we must also encourage chastity in the church and the world in addition to refraining from lustful intent in the heart (Matt. 5:27–28). In fact, the apostles elsewhere give us this precise command (1 Tim. 2:8–10; Heb. 13:4). Male and female alike, we violate the command against adultery and do not love our brothers and sisters in Christ if we act and dress in a manner that might provoke another to stumble into lust (Rom. 14:13–23; 1 John 4:21).
Jesus is teaching us the end to which the command against adultery points. Since, as the church father Jerome said, “what we conceive in the mind we might complete with an act” (Commentary on Matthew, 1.5.29), it is not enough to refrain from the physical act of fornication (Matt. 5:27–28). God’s law, our Savior shows us, has a pure heart as its final goal. The pursuit of this purity is to be among our most urgent tasks, and we must do whatever it takes to keep our minds free from lust’s pollution (vv. 29–30).
Unfortunately, lust is rampant in the church today, and many are in bondage to pornography and other sexual sins. If this is a problem for you, cut off your access to outlets where you may find temptation. Whether or not lust has a particularly strong grip in your life, consider how you dress and act in the world and in the church. Are you a stumbling block for others with revealing clothes or with a flirtatious personality?
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