NOTES for Mat 12:1-21
The scribes' accusations against Jesus are very serious: He is profaning the Sabbath, He is doing what must not be done, and "must not" in the highest, sacred sense - this is a violation of a divine commandment. Christ does not justify Himself; instead, He reminds them that King David once also did what was not permitted, and that even now the priests profane the Sabbath, and this profanation took place and still takes place in the Temple itself! Jesus deliberately uses such words, though He could have spoken more mildly. And if those violations seem forgivable to the scribes, what will they say if the One who is here is greater than David, greater than the priests, and greater than the Temple?
Christ shows them His divine-human freedom to do good on the Sabbath, the sacred day of God's perfection. The prohibition exists only so that human freedom will not be turned toward evil, toward destruction and death. This means that Jesus' actions announce that standing before them is the One who is incapable of evil: the Lord of the Sabbath.