What is Jesus' attitude towards the Mosaic Law as presented by Matthew (Mt. 5) ? Why is this significant?

Jesus' attitude towards the Mosaic Law as presented by Matthew (Mt. 5) is:

"Not to destroy" (Matthew 5:17). Jesus' teachings seemed radical to His contemporaries. It was natural that they would feel threatened by the young prophet from Nazareth, whose fame was spreading rapidly. Till heaven and earth pass away, one jot or one tittle will by no means pass from the law till all is fulfilled. Whoever therefore breaks one of the least of these commandments, and teaches men so, shall be called least in the kingdom of heaven; but whoever does and teaches them, he shall be called great in the kingdom of heaven.

"But to fulfill" (Matthew 5:17). Rather than setting out to destroy the Law (a term frequently used of the entire works of Moses, and of the Old Testament as a whole, as well as of the commandments embedded in them), Jesus came to "fulfill" the Law. Western commentators have discussed how Jesus fulfilled the Law. Some have taken this statement to mean that Jesus kept the Law perfectly. Others have suggested it means that Christ fulfilled the prophecies the Old Testament contains. But Jesus' listeners understood exactly what Christ meant. For it was the desire of every sage and rabbi to "fulfill" the Law, in the sense of explaining it's true and complete meaning.

With this introduction, and with Jesus' clearly stated confidence in the Old Testament as the authoritative Word of God, Jesus was ready to unveil the Law's true import.

In this reinterpretation of the Law, Jesus laid a foundation for our need of His redeeming work. If God judges not only our actions but the thoughts and motives of our hearts, we must be changed within. And while law can regulate behavior, the law can never transform the human heart.