Jesus said he did not come to abolish the Law and the Prophets, he came to fulfil them. One way of seeing the difference is to compare the opening verses of Chapter Twenty-Four of Exodus with the opening verses of Chapter Five of Matthew’s Gospel.
In the opening verses of Chapter Twenty-Four of Exodus, Moses had the people sit below, as he went up on Mount Sianai, where he gathered the leaders of the tribes around him.
In the opening verse of Chapter Five of Matthew’s Gospel, Jesus had the people sit below as he went up the mountain side, gathering the Apostles around him.
In that chapter of Exodus, Moses inaugurated the Old Law with the one-liners we call the “Ten Commandments.” In that fifth chapter of Matthew’s Gospel, Jesus inaugurated the New Law with his one-liners we call “The Beatitudes.”
While the Ten Commandments tell us what we must avoid to become good people, the Beattitudes fulfill their promise by telllng what we must do to fulfill the promise of the Ten Commandments.