Jesus made some statements in the Sermon on the Mount addressed to the Pharisees that would be in sharp contrast with the Old Testament Law. Even though the fundamental Law was the 613 commandments within the Torah, the common understanding of it expanded to the entire Old Testament by the time of Jesus’ first advent. During the early Second Temple period the religious authorities had left Old Testament Mosaic Law in favor of Rabbinic Judaism. Rabbinic Judaism is based on a man-centered philosophy. It also tied people up with so many conditions and rules there was no way a Jew could ever fulfill them. It would have been easy to conclude that Jesus wanted to abolish the Law that had been given through Moses, but Jesus assured his listeners that He had no such intention.
He fulfilled the prophecies of the Old Testament by doing what those prophecies said the Messiah would do. He also “filled up” the law by pouring into it the meaning that had been forgotten by the teachers of Israel. This is what the Sermon on the Mount was teaching, that is, the intent of the Law. He applied the Law to thoughts and motives as well as to actions.
He also fulfilled the Law by accomplishing what the Law had failed to do. The Law revealed the standard of righteousness that God expected. The Law also revealed to people their sinful state and let them know that they were sinners, and their efforts were insufficient to earn eternal life (Romans 3:19, 20). The Law pointed out the need for a Savior, thus it served as a means “to lead us to Christ that we might be justified by faith” (Galatians 3:24).