Please let me repeat myself: the expression is "the law and the prophets", and it means the whole of the Hebrew Scriptures (which were not at that time canonised). All of them, not just "the Law" (meaning the Pentateuch).
These Scriptures were replaced by the good news of the "kingdom of God", ushered in at the baptism of Christ by John the Baptiser. The "kingdom" was the most common topic on Jesus' tongue, because it refers to the rulership possessed by God. It is not a rulership possessed by any man or group of people. A relationship with God is not obtained through legalism or prophecy but in a dynamic living direct relationship with the kingdom/kingship of God. It is not euphoric, or emotional, it is factual and forensic, based solely on faith. Jesus was giving his kingdom message to those people, his hearers. They could adopt it then and there, while he was speaking with them.
Much of what we call the "Hebrew Scriptures" (OT) was written and edited during and after the Babylonian Exile. The people wanted to understand why God's chosen people had been treated like this. These exiles -- who were the elite and powerful of Judah, not the "people of the land" -- decided they had been exiled because the Israelites and Judahites had not followed the Commands and Laws, and this is what they wrote and what coloured their written record. So when the descendants of this upper echelon returned to the people of the land who had been left in Judah by Nebuchadnezzar, the elite set about imposing their will upon the people, to force them into a legalistic regime of obeying laws and commands. That is what Jesus wanted to bring to an end: the "law and the prophets" did not give life.
I believe that Jeremiah was a prophet more to the people of the land, as against the priestly class in the cities and in the Temple at Jerusalem. He spoke about a heart relationship with God, in which the laws are written within a person. When Jesus Christ ministered, he worked with the "people of the land", not with the upper echelon. He spoke like Jeremiah did.
Doug