Jesus didn’t just know the law, as the Messiah, he embodied it, he was the law.  The Pharisees knew that the Messiah was to come from the house of David, so would be a son of David, but they expected a human king, a powerful warrior that would free the people from oppression by foreign powers.  They did not expect the Messiah to be God himself standing before them in the human person of Jesus.  This did not enter their realm of thinking or understanding; they were not open to who Jesus was or to his message.  As I already mentioned, Jesus embodied the law so his focus was on actions, on living God’s truth, as opposed to just words.  The commandments were intended to teach people how to live life well rather than to be used for the purposes of judgement, self-promotion or to impose control on the lives of others.  Jesus had not come to oppose the law of the prophets but to uphold and fulfil them, to interpret them in ways that make them meaningful based on God’s truth not human world views.