The Pharisees were not a bunch of old legalists. The Pharisees were a grass roots, unofficial pressure group who passionately wanted to purify Israel so that they might prepare the way for God's Kingdom to come. And the Pharisees were also a popular movement. One of the reasons that the Pharisaic movement was popular was because the High Priestly class in Jerusalem was made up of mostly Sadducees who were largely considered to be compromised with Roman power and disloyal to the Jewish identity and calling. The Pharisees were people reacting against this compromise and disloyalty, hence their emphasis on purity. However, the Pharisees felt their own influence being threatened and rivaled by Jesus and they were determined to re-gain the upper hand on the culture. That is why they began to question and challenge him in public. And as NT Wright points out, the question at hand in Luke 6 is not really about Sabbath keeping but about authority. How does Jesus think He is to go about His work of bringing God's Kingdom without first seeking the approval of the most influential community leaders? Jesus didn't subject himself to the authority of the Pharisees to determine whether or not He was a good Messianic candidate and this fact appears to have infuriated many of them. The growing animosity of the Pharisees and their plotting led Jesus to return to a place of prayer to gather strength for the intensifying battle ahead. When Jesus returns after His night in prayer, He comes with a new resolve. It is at this point that Jesus identifies twelve disciples to symbolize the renewed Israel that He is constituting around Himself and as He descends from the mountain where he had gone to pray (like Moses) He brings with Him a renewal of the covenant. It appears that the renewal of Israel is in fact already taking place because unlike Moses who descended from the mountain of God only to find a wild and idolatrous people, Jesus descends to a crowd which is pressing around Him for his cleansing and healing touch.
Jesus then pronounces the blessings and the curses associated with this new covenant as Moses did with the first covenant in Deuteronomy 27-28. And these blessings and curses are somewhat counter-intuitive to much of what the Pharisees envisioned concerning the Kingdom of God and the renewal of the covenant. In fact, the rest of the chapter will be teaching about Jesus' vision of the Kingdom of God as opposed to other visions, not least, the Pharisees. The Pharisees had come out to challenge Jesus' authority because He was treading on their territory. Jesus' response was to reassert His authority and to add His critique of the Pharisees vision. But He does it in a very wise way, not by starting a character defamation campaign but by upstaging the Pharisees vision on point after point. In the end, many among the crowds would conclude that Jesus' vision of the Kingdom was more compelling and more faithful to what was promised through the Torah. But for those who had already made their decision against Jesus, His words were insufferably offensive. It is a sad fact that often the things we react against most harshly are also crimes we often end up committing ourselves. The Pharisees established themselves as a resistance movement to a corrupt, power-protecting, Sadduceean leadership but they did not like it when Jesus established another reformation that threatened the accumulated power and influence of the Pharisees. But while it is the truth that sets us free, it is also the truth that continues to challenge us to a higher calling, no matter who we are or what cause we support or have given our lives too. The Kingdom of God has arrived in Jesus and it is a challenge to everyone whether Sadducee or Pharisee, Jew or Gentile, Christian or Atheist. As Luke told us earlier in His gospel, even Mary, the mother of Jesus, would experience the sharp division between lies and truth in her own soul. Jesus never ceases to be exciting as well as controversial.