Jesus' Sermon on the Mount recorded in Matt 5-7 is one of the most familiar areas of Jesus' teaching. I say that because it contains a lot of what many people might crudely regard as the greatest hits of Jesus' teachings (The Lord's Prayer, love your enemies, judge not lest ye be judged, the golden rule, etc.). Two sections that have puzzled many people are Jesus' teachings on anger and lust. Both of these follow the typical pattern of "you have heard it said... but I say to you" that you'll find throughout the Sermon on the Mount. Yet, what is unique about these two sections is how Jesus equates anger and lust with murder and adultery (the sixth and seventh commandments). But why?
The immediate answer is that Jesus is concerned with the heart first and foremost. That is not to say that he isn't concerned with actions. Rather, he is aware that actions are begotten by the heart (Luke 6:45). They don't stand alone by themselves. Yet, one might still be puzzled why Jesus makes such intense comparisons. Truly not all people who are angry have a desire to murder, right? This precise dilemma is where our friend C.S. Lewis comes in.
Proper Rewards-Proper Consequences
In The Weight of Glory, Lewis keenly observed that there is such a thing as a proper reward for an action, desire, or disposition. There are also improper rewards for actions, desires, and dispositions. He illustrates this by the image of the lover and marriage,
“Money is not the natural reward of love; that is why we call a man mercenary if he marries a woman for the sake of her money. But marriage is the proper reward for a real lover, and he is not mercenary for desiring it.”
If one were to say that he is committed to his fiancé because her parents have a lot of money, we would be right to be disgusted. However, if one were to say that his committed to his fiancé because he desires marriage, we would not. Why are we disgusted by one and not the other? It is because marriage is the proper reward for the lover. We might even say that, for the lover, dating and engagement are in their very essence penultimate to the ultimate which is marriage (though we would further say that marriage itself holds a penultimate quality as an image to Christ and the church). Dating and engagement find their final and full expression in marriage.
This realization of proper reward is of great value when we turn to interpret the sermon on the mount. Just as marriage is the proper reward for the lover, so murder is the proper reward (or perhaps proper consequence) for the angry man. The angry man does not find the fullest expression of his angry desires until murder is executed. Unrighteous anger is penultimate to the ultimate of murder. The same goes for lust. What purpose does lust have but to give way to adultery? Adultery is the proper consequence for lust.
And so, it does make good sense for Jesus to make the equations with anger and lust. Were it not for God's common grace in restraining sin, every angry man would be a murderer and every lustful man would be a serial sex offender.
This paradigm is very helpful when it comes to understanding our own hearts. Where do our sinful desires point to? What are our desires penultimate to? We might say that the sinful obsession of recognition and glory is penultimate to breaking the first and second commandments. Left to my own devices, the desires of my heart would not be noble to grant. In fact, it is not until God reorders our desires (a both one time and lifelong process) that we can truly delight in the Lord and thus have desires that are noble to be granted (Psalm 37:4).