I have copied the verses into the blog for your reading. It is important that we all read the same thing. This is where Jesus starts the process of making the Pharisees look foolish and they started to plan Jesus death.
Mat 12:1 At that time Jesus walked through the grain fields on a Sabbath. His disciples became hungry and began picking heads of grain to eat. Mat 12:2 When the Pharisees saw this, they told him, "Look! Your disciples are doing what is not lawful to do on the Sabbath!" Mat 12:3 But he told them, "Haven't you read what David did when he and his companions were hungry? Mat 12:4 How is it that he went into the house of God and ate the Bread of the Presence, which was not lawful for him and his companions to eat but was reserved for the priests? Mat 12:5 Or haven't you read in the Law that on every Sabbath the priests in the Temple violate the Sabbath and yet are innocent? Mat 12:6 But I tell you, something greater than the Temple is here! Mat 12:7 If you had known what 'I want mercy and not sacrifice' means, you would not have condemned the innocent, Mat 12:8 for the Son of Man is Lord of the Sabbath."
The Pharisees are trying to have Jesus admit that he and his disciples had broken the law. I love it when Jesus uses the verses from the books that the Pharisees were supposed to be experts. The first answer was based on Deuteronomy 23:25. Which indicates they were not stealing? The Pharisees based their accusations on Exodus 34:21. This verse says that you should not work on the Sabbath. The disciples were not harvesting as the Pharisees said. They were picking a few kernels for something to eat. Harvesting would be stealing. They were allowed to do that by the old law in Deuteronomy 23:25.
Mat12:9 Moving on from there, Jesus went into their synagogue. Mat 12:10 Suddenly a man with a paralyzed hand appeared. The people asked Jesus if it was lawful to heal on Sabbath days, intending to accuse him of doing something wrong. Mat 12:11 But he asked them, "Is there a man among you who, if he had one sheep and it fell into a ditch on the Sabbath, wouldn't take hold of it and pull it out? Mat 12:12 How much more is a human being worth than a sheep! So it is lawful to do good on Sabbath days." Mat 12:13 Then he told the man, "Hold out your hand." He held it out and it became normal, as healthy as his other hand. Mat 12:14 The Pharisees, however, went out and plotted against Jesus to kill him. Mat 12:15 When Jesus became aware of this, he left that place. Many crowds followed him, and he healed all of them, Mat 12:16 ordering them not to make him known. Mat 12:17 This was to fulfill what was declared by the prophet Isaiah when he said, Mat 12:18 "Here is my Servant whom I have chosen, whom I love, and with whom I am pleased! I will put my Spirit on him, and he will proclaim justice to the gentiles. Mat 12:19 He will not quarrel or shout and no one will hear him shouting in the streets. Mat 12:20 He will not snap off a broken reed or snuff out a smoldering wick until he has brought justice through to victory. Mat 12:21 And in his name the gentiles will hope."
The Pharisees are trying another trap. They were trying to find a way to accuse Jesus. The healing of the man’s hand was what the Pharisees considered work. So Jesus made them think about it. They had to answer the question of the lost sheep which they knew any shepherd would do. Then they had to decide if a man was worth more than a sheep. Jesus then told the man to hold out his hand. When he did so it was healed. This amazed the crowds but I am sure the Pharisees were infuriated. This was done also to fulfill a prophecy in Isa 42:1-4. My thoughts on this were they also had to explain that Jesus healed a man's hand. They could non duplicate that.
There is so much more going on in these verses that it would be worth your time to investigate on your own.