Part of the Sermon on the Mount covers the topic of adultery. Nothing unexpected here: Jesus is against it. In fact, he is even against lust. That is not too unexpected either. He uses rather strong language; he speaks of gouging out your eye and throwing it away. That is a little unexpected language, but then, preachers have been known to get ramped up about sin. Here is what is unexpected: the reason he gives for avoiding adultery and lust: “It is better for you.” He says it twice. The motive he appeals to is self-interest. He doesn’t ask us to deny self-interest. He asks us to maximize self-interest. Religious teachers hardly ever do that. Very unexpected. Jesus repeats this theme in Matthew 18. Notice again the strong language and notice again the reason Jesus gives for avoiding sin:
Matthew 18:8-9 (NIV) If your hand or your foot causes you to sin cut it off and throw it away. It is better for you to enter life maimed or crippled than to have two hands or two feet and be thrown into eternal fire. 9 And if your eye causes you to sin, gouge it out and throw it away. It is better for you to enter life with one eye than to have two eyes and be thrown into the fire of hell.
Two more times Jesus says, “It is better for you.” Jesus was all about what was better for us. He didn’t ask us to be good just because or because it would make God happy or glorify God. All those things are true, but expected. What is unexpected is the appeal to self-interest: it will be better for you.