The law of Moses was a lower law that was given to the Israelites by Jesus, who is the Great I AM or Jehovah. When Jesus came to earth for his ministry he did not do away with the law of Moses but fulfilled the law of Moses which was his own law.
Matthew 5:17-18
17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.
18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
In fact, read the entire sermon on the mount to see how Jesus does not destroy the law of Moses but fulfills it.