"When we compare [Matthew's] teachings to the halakic rulings of the Mishnah or the detailed regulations for community life codified in the Community Rule of the Qumran covenanters (1QS), we can hardly help noticing the rather broad and incomplete character of Matthew's programmatic presentation [in the Sermon on the Mount]. As Wayne Meeks observers,
... [W]e have here no system of commandments. The rules are exemplary not comprehensive, pointers to the kind of life expected in the community, but not a map of acceptable behavior. Still less does Matthew's Jesus state philosophical principles from which guidelines for behavior could be rationally derived. We are left with the puzzle that while Jesus plays the role of a conventional sage in Matthew, his teachings recorded here do not add up to an ethical system. It is not in such a program of teaching, apparently, that Matthew understands the will of God to be discovered.Matthew's rigorous summons to moral perfection cannot be rightly understood as a call to obey a comprehensive system of rules. Despite his emphasis on the church's commission to teach obedience to Jesus' commandments, Matthew sees such teaching as instrumental to a deeper goal: the transformation of character and of the heart." (98)
Really, I could quote most of Hays' chapter on Matthew. Each succeeding section unfolds another aspect of the ethics constructed by Matthew's narrative world so foundational, so basic to Matthew's vision, that I wonder why I've never seen it before.
For instance, the next section on the "hermeneutic of mercy" and the twice repeated (!) citation of Hosea 6.6 (Mt 9.13; 12.7) bowls over some of my gut-assumptions about Matthew. The high obedience ethic of the Gospel and the paltry character of "mercy not sacrifice" appeals in much contemporary literature.
Another money quote:
"In these passages [Mt 9.13 and 12.7] we see the outworking of Matthew's earlier claim in the Sermon on the Mount that Jesus fulfils rather than negates the Law. When that formula is applied to test cases, such as eating with sinners and harvesting grain on the Sabbath, we see that the Law is understood to bear witness to what Matthew elsewhere calls 'the weightier matters of the law: justice and mercy and faith' (22:23). Jesus' teaching provides a dramatic new hermeneutical filter that necessitates a rereading of everything in the Law in light of the dominant imperative of mercy." (100)
This is a beautiful chapter.