In the spring I took a seminar in Biblical Theology. One of the papers I wrote was on Jesus and the Law of Moses, specifically trying to untangle Matt 5:17-20. If you are interested in reading the paper, you can find it here. This was the conclusion I came to:
The conclusions of this study are as follows. First, as section III demonstrated, Jesus fulfills the normative and commanding aspects of the Law and the Prophets by means of his teaching. This is not so much to say that Jesus’ ethic is vastly superior to the OT ethic, as it is to say that Jesus’ teaching plays a role in the age of fulfillment that is analogous to the role that the Law and the Prophets played under the “age of promise.”
Second, Jesus’ fulfillment of the OT is not viewed in terms of “transcending,” “radicalizing,” or “internalizing” the OT. Jesus’ teaching is seen to be in continuity with the OT (though no doubt with its own emphases and changes appropriate to the age of fulfillment).
Third, the differences between the OT laws and Jesus’ commandments seem to highlight especially 1. a difference in the primary locus of authority (Jesus versus Torah), and 2. differences in emphasis that have to do with the differing nature of the two divine economies.
Approaching the rest of the Bible, these conclusions have the following two implications. First, if Jesus is the primary locus of authority under the present economy, then the words of Jesus and his apostles are the starting point for instructions regarding life with God in the “age of fulfillment.” As Graeme Goldsworthy says, “no longer is it Moses on Sinai that is the beacon to guide us; rather it is Christ on Calvary. When the Ephesians needed warning over the temptation to go on living as ‘gentiles,’ Paul does not rehearse the Ten Commandments, but he says, ‘That is not the way you learned Christ’” (Preaching the Whole Bible as Christian Scripture, 160). This is supported by other passages in the New Testament. For example, Rom 7:4–6 portrays the believer as “dead” or “released” from the Law Covenant and joined to Christ. Paul seems to have a concept of a “Christ-Torah” that consists of Jesus’ actions and teaching that serves as the basis for Christian ethics (1 Cor 9:21; Gal 6:2). Paul also speaks of believers “fulfilling the law” by the Spirit through love, which seems to imply living out the righteousness set forth in the Law without being under the yoke of the Law (Rom 8:4; 13:8, 10; Gal 5:14). Similarly in the NT, Christ’s life becomes a pattern to follow in such a way that he himself becomes “the way” for his followers (John 13:34–35; 14:6; Eph 4:20; 1 Pet 2:21–23).
Second, if Jesus is not “transcending,” or “radicalizing,” or “internalizing” OT laws but rather teaching in such a way that is consistent with the ethical demands of the OT, then we should see the OT and NT as mutually informing. While Christ fulfills the OT, the OT explains Christ. They are both mutually interpreting and mutually supporting. While we see the revelation of God in Christ and through the apostles as the primary locus of authority, for instructions for living under the New Covenant, “until heaven and earth pass away, not the smallest letter or stroke shall pass from the Law until all is accomplished” (Matt 5:18). The OT remains God’s inspired word to us, and it is “profitable for teaching, for reproof, for correction, for training in righteousness; so that the man of God may be adequate, equipped for every good work” (2 Tim 3:16–17).