Why "law" is permanent

The clerics of Jesus’ day did not understand how he could live as he did, yet claim to be in compliance with religious law. He actually healed on the Sabbath; he associated with the ceremonially unclean, his disciples didn’t fast ­— it was contrary to what the Pharisees taught about how a proper Jew should live. On the day he went up the hillside to teach the crowd (we call it the Sermon on the Mount) he explained his relationship to the law:
       “It is not my intention to do away with the sacred Law of Moses (or the prophetic writing). They are permanent and will last forever. Each single bit of the law – the smallest letter and even a tiny little part of that letter ­­– will continue until it is all fulfilled. By “fulfilled” I mean, “perfectly realized in the life of all who take my name, Obviously that would not be perfect compliance with a set of legal statements, but it would involve an inner transformation that couldn’t help but expresses itself that way. When that happens, the law becomes a description of how you are living, not an expectation of how you ought to live. So the answer to your concern is that I did not come to abolish the law but to fulfill it as intended. Law is description of the nature of God. Since our goal is to become like him, and he never changes, it follows that law is permanent.
       Obviously you do not understand my role in demonstrating how a believer can live in relationship with laws laid down that by Moses. In simple language, I came to show the kind of life those laws were intended to produce. Law plays a vital role in moral development by laying down a set of regulations that point the kind of life that pleases God. “Thou shall not kill” is not a rule to govern how you ought to live. It represents a stage of moral development achieved not by external obedience, but by a change of heart – a result not a restriction. “Thou shall not commit adultery” is not a social regulation like “Don’t leave your camel in the street.” It reveals a desired condition, but does not empower you to achieve it. The answer to how it comes about involves something quite different. It has to do with a change of heart. Law is a signboard describing the direction you should take in order to be the person God desires; not a set of directions helping you to become that person.
      Law is forever because it expresses the nature of God, and God is eternal. Sinless perfection is not something we accomplish, but something God declares to be true in Christ Jesus. In a secondary sense it is something we are displaying as the Spirit continues his cleansing work in our life.