Six times in the Sermon on the Mount (SOTM) Jesus says something like, “You have heard it said _______, but I say to you _______.” This all follows Jesus’ main point for the SOTM from Matt. 5:17-20, “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them…for I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven.” Jesus looks to the teachings of the Pharisees and scribes, what his audience had heard said, as an incomplete picture of God’s covenantal Law with his people. Where the Pharisees had applied the Law to only what people did or said, Jesus wanted to apply it to their thoughts and emotions. Where the Pharisees had opened loopholes for nominal obedience, Jesus wanted to seal them shut.
And in Jesus’ thesis statement, “I have not come to abolish them but to fulfill them,” we see that this fully fleshed-out obedience stems from the incarnate God himself. Only Jesus fully fulfilled the Law, so his command to obey the Law comes from the standpoint of his own obedience, not the best interpretations of a sinful person like the Pharisees. And, thankfully, in faith we enjoy Jesus’ standing before God, so these efforts in obedience aren’t to save ourselves but to keep in step with our Savior.
So in these six statements Jesus gives us examples of obeying God fully, but these sermon illustrations are also meant to be followed. So when it comes to lust and adultery (and vows and revenge and so forth, as we’ll get to in coming weeks), these are Jesus’ legitimate thoughts on the matter. Adultery is perhaps fed by many streams, but lust is its ultimate source, so Jesus goes after the real heart of the problem and deals with both adultery and lust simultaneously. So Jesus is certainly interested in your external life and how we reflect God to the world, but he’s also very much interested in your internal life, since “out of the abundance of the heart” flows all that we do.(Luke 6:45)
Interestingly, when it came to lust and divorce, Jesus was being pretty conservative and then pretty liberal. To his command to not even glance at a woman inappropriately, his audience maybe thought him a prude. They would’ve looked for similar excuses we use for all sorts of sin, “but it’s not hurting anyone,” “this is just what people do,” “it’s not cheating if it’s just in my head.” I’m sure they thought he was quite the buzzkill in the moment.
But then he followed that up with a very liberal move, the prohibition of casual divorce. He doesn’t prohibit it unilaterally, it’s important to see, but he permits the severing of the marriage covenant only when all boundaries of the covenant have already been broken by adultery (permits but doesn’t require, we might add). In our time we might read that as still pretty prudish, but this was incredibly progressive for his time, and actually concerned women’s rights just as much as it was about marriage and adultery. Today, men keep women in abusive marriages to maintain patriarchal control, but then women were sometimes divorced for the smallest of offenses, the threat of which was used to keep a woman under her husband’s thumb. A divorced woman wore the social stigma of her divorce, had limited economic means, and might not have much opportunity for recourse other than marrying again and enduring the same threat of divorce, again. And Jesus refuses to let his children treat each other this way.