Matthew 12:14 The Pharisees plotted Jesus' death because they were outraged. Jesus had overruled their authority (Luke 6:1) and had exposed their evil attitudes in front of the entire crowd in the synagogue. Jesus had showed that the Pharisees were more loyal to their religious system than to God.
Matthew 12:15 Up to this point, Jesus had been aggressively confronting the Pharisees' hypocrisy. Here He decided to withdraw from the synagogue before a major confrontation developed because it was not time for Him to die. Jesus had many lessons still to teach His disciples and the people.
Matthew 12:16 Jesus did not want those He healed to tell others about His miracles because He didn't want the people coming to Him for the wrong reasons. That would hinder His teaching ministry and arouse false hopes about an earthly kingdom. But the news of Jesus' miracles spread, and many came to see for themselves.
Matthew 12:17-21 "The people expected to be a king." This quotation from Isaiah's prophecy (Isaiah 42:1-4) showed that the Messiah was indeed a king, but it illustrated what kind of king - a quiet, gentle ruler who brings justice to the nations. Like the crowd in Jesus' day, we may want Christ to rule as a king and bring great and visible victories in our lives. But often Christ's work is quiet, and it happens according to His perfect timing, not ours.
Matthew 12:24 The Pharisees had already accused Jesus of being in league with the ruler of the demons. They were trying to discredit Him by using an emotional argument. Refusing to believe that Jesus came from God, they said He was in league with satan. Jesus easily exposed the foolishness of their argument.