Jesus begins by making it clear he is not abolishing the Law, but rather demonstrating how to keep the Law properly. It is possible, Scot McKnight suggest, that Jesus has been accused of breaking the Law or teaching things which nullified the Law. There are several examples of the Pharisees questioning Jesus about certain practices such as eating with sinners (Matt 9:1-11), fasting (Matt 9:14), and Sabbath (Matt 12:1-13).
The word fulfill in in contrast to annulling the Law, “far from undercutting the role of the Law and the Prophets, is to enable God’s people to live out the Law more effetively” (Nolland, Matthew, 218). For Jesus the Law is God’s eternal word. The heaven and earth itself will pass away before the Law does.
Jesus is not abolishing the commands of the Law at all. The righteousness of the true disciple of Jesus must exceed even the Pharisees. The Pharisees were known for “building a wall” around the Law so that they would not break the Law in ignorance. For example, the Law did not require a tithe on herbs such as mint, dill, or cumin. But the Pharisee tithed on everything, including these plants. Later in Matthew Jesus will call this “straining out a gnat but swallowing a camel” (Matt 23:23-24).
Sometimes the Pharisees are mis-characterized as hyper-legalists who demanded all Jews following their interpretation of the Law. Contemporary preaching makes them sound like Puritans (or the men from A Handmaid’s Tale). It is important to understand the motivation for much of the teaching of the Pharisees: they wanted to obey the Law since it was God’s holy and perfect will. They did not obey out of fear, but as a response to God’s grace given to all Israel. For a Jew living in the Second Temple Period, the Pharisees were not the “bad guys” (in contrast to contemporary Christian preaching).
To have “more righteousness than the Pharisees” does not mean “have more rules than the Pharisees.” They increased the number of rules and traditions to build their wall around the Law, Jesus wants his disciples to seek the heart of the Law. What are the principles found in the Law which reflect the heart of God? What are the principles behind a particular command which God demands of his people at in time in salvation history?
Scot McKnight suggests this section of the Sermon on the Mount is a new way of reading Scripture. For McKnight, Jesus is setting himself up as a lens through which Scripture should be read. Jesus “had the audacity to think he was the messiah and taught a Messianic ethic” (Sermon on the Mount, 67). This messianic re-interpretation of the Law was radical and resulted in conflict with the Pharisees and other religious leaders. Imagine if Jesus showed up in a typical Bible College or Seminary classroom (or a plenary session at the Evangelical Theological Society) and told the professors they were reading the Bible wrong and were “blind guides”(Matt 23:16) or hypocrites who look good on the outside but are “full of hypocrisy and wickedness” (Matt 23:27-28). I am certain they would question Jesus in the same way the Pharisees did (Where is your authority? Where did you get your degree? Where are your scholarly publications?)
This is not a kind of “find Jesus in the Old Testament” hermeneutic. Jesus fulfills the entire theological story of the Old Testament. He is the climax of the story since everything in the Law and prophets point towards him.
Jesus really is teaching his disciples how to understand the Law and apply it in a new context (like the Pharisee), but not by multiplying commands. Jesus demands his disciples go deeper than a list of rules and seek the true heart of God behind the Law. He will give two examples of this new way to read the Law in the next two paragraphs of the Sermon on the Mount by re-reading two of the Ten Commandments.