What is lawful on the Sabbath

“How much more valuable is a man than a sheep! Therefore it is lawful to do good on the Sabbath.” Matthew 12:12
Time and time again Jesus came into conflict with the Pharisees over what they perceived to be Him breaking the Sabbath law. In the Torah, there were several things listed that you could not do on the Sabbath: work (Ex. 20:10, 31:14-15, Lev. 23:3, Deut. 5:14), lighting fires (Ex. 35:3). However the rabbis in their zeal to not be found guilty of breaking these commands, instituted extra layers of commands concerning the Sabbath day. You could not cut your hair on the Sabbath, because that was considered work. You could not wear false teeth on the Sabbath, because that constituted bearing a burden, which was considered work. You could not spit on the ground on the Sabbath, because that would irrigate the soil, which was considered work. If you were a doctor, and a patient was brought to you on the Sabbath, you could prevent the person from dying, but you could not do anything to aid the healing process, because that was considered work. It is this latter point that the Pharisees tested Jesus on by bringing him a man with a withered hand, to see if He would heal him on the Sabbath.
But Jesus would have none of this. He pointed out their hypocrisy: they would rescue a sheep of theirs on the Sabbath if it fell into a pit. But they would judge Him for healing a man on the Sabbath. Their attitude placed the comfort of a sheep above the welfare of a human being. To answer their question, ‘Is it lawful to heal on the Sabbath?’ Jesus answered, ‘It is lawful to do good on the Sabbath.’ This was not an issue only about healing, because earlier in the same chapter He had defended His disciples who had been caught ‘working’, by picking grain, rubbing it in their hands (thus, ‘harvesting’ and ‘threshing’) and eating it. Jesus’ point was this: human need is more important than ceremonial regulations.