You should notice some repetition in chapter twelve. A man struck dumb by the devil is brought to Jesus, a story similar to one told in chapter nine. In both cases, Jesus opponents attribute the Lord’s power to the devil. Also, Jesus’ reference to Hosea 6:6 is repeated in chapter twelve. The Pharisees request a “sign” from Jesus, a miracle, and yet the miracles they have seen they have refused to believe. They will request another sign in chapter 16 and again, Jesus will refer them to the “sign of the prophet Jonah,” a veiled reference to Jesus’ resurrection.
Here’s the major point of the chapter: Jesus has great authority, greater than anyone on earth. He is “Lord of the Sabbath,” a title belonging only to God. He is greater than Solomon, and greater than the temple. He proves his position by arguing his case from the law itself, indicating his superior knowledge of it. He also proves his position by the miracles he performs, and by the one that will be performed with his resurrection.
He also proves it by the manner of his ministry: he cares about people, exalting ministry to the needy over punctilious attention to legal detail. Finally, Jesus proves his authority by the way he conducts his ministry: he’s not a glory hound, despite the fact that he has every right to the popularity he’s receiving. Jesus urges people to keep things quiet, which Matthew (and only Matthew) records is a trait of the servant of the Lord (12:18-19, citing Isaiah 42:1-4).
So here is a prescription for ministry, taken from Jesus’ life: First, keep the law (God’s law), but make sure it is the law you are keeping and not some traditional interpretation of the law. You cannot have a relationship with God without obedience (vs. 50). Second, focus on helping others. Everything in the law has to do with love for God and for others (which Jesus will make plain in 22:40). One cannot love God and ignore the needs of mankind. Third, pay attention to the kind of person you are as evidenced by the things you do. A good person consistently does good things because he wants to do them. A bad person does not. Finally, the disciple does not follow Jesus to get attention. He follows Jesus quietly and his service is between him and the God he serves.