Reading this passage today made me want to research it. Jesus is Lord of the Sabbath, and He came to fulfill the law not break it. This passage has several aspects that are best read together as Jesus combines them:
Jesus and Disciples Pluck and Eat Grains on the Sabbath
At that time Jesus went through the grainfields on the Sabbath. And His disciples were hungry, and began to pluck heads of grain and to eat. And when the Pharisees saw it, they said to Him, “Look, Your disciples are doing what is not lawful to do on the Sabbath!”
The Law is concise about the Sabbath (Lev. 23, Duet. 5) and makes a general statement not to work. Plucking grains on your neighbor's property was permitted by the Law (Duet. 23).Reading the Law at face value, the disciples were not breaking Biblical law, but Rabbinical Law. Reaping is one activity forbidden on the Sabbath based on the Misna Shabbat.
David Eating the Showbread
But He said to them, “Have you not read what David did when he was hungry, he and those who were with him: how he entered the house of God and ate the showbread which was not lawful for him to eat, nor for those who were with him, but only for the priests?
Jesus states that David eating the showbread was unlawful, as it was lawful only for priests for eat the showbread per Biblical Law. One can either read this passage as Jesus then condoning breaking Biblical Law because David was hungry or that Jesus was highlighting the inconsistency of His opponents. Since Jesus came to fulfill the law and obeyed God in everything He did, it is more likely that the latter reading is accurate, especially considering how serious God took priestly matters.
With this interpretation, The Pharisees revered David and possibly did not condemn him for his eating of the showbread. Jesus asks then why they condemn Him and his disciples when they did not break the law.
Both King Saul and King Uzziah were punished by God for acting as priests. It is clear that God showed mercy on David in that situation. Nothing in Samuel indicates that David was esteeming himself as a priest by eating the showbread but rather eating due to hunger.
Priests Working on Sabbath
Or have you not read in the law that on the Sabbath the priests in the temple profane the Sabbath, and are blameless?
Jesus is speaking with hyperbole saying that the priests profaned the Sabbath by working on the Sabbath to point out that even all work was not forbidden on the Sabbath. The priests and Levites were assigned altar duties, and later in Numbers, God calls for a Sabbath offering (Num. 28).
Jesus is Lord of the Sabbath
Yet I say to you that in this place there is One greater than the temple. But if you had known what this means, ‘I desire mercy and not sacrifice,’you would not have condemned the guiltless. For the Son of Man is Lord even of the Sabbath.”
As Jesus often does in addressing others' questions or comments towards Him, He uses this situation to make a statement about Himself or the kingdom of God. Jesus declares that He is greater than the temple and is "Lord even of the Sabbath." Yet as Lord of the Sabbath, Jesus does not break the Law or condone breaking the Law. Jesus clearly had respect for the Law (Matt. 5:18).
- Jesus and His disciples were not breaking Biblical law by plucking grains to eat and satisfy their hunger in the moment. The Sabbath law required some interpretation since it was general, and Jesus interpreted it as allowing the actions of Him and His disciples.
- David's action was unlawful to eat the showbread, but he did claim to keep himself and men holy beforehand. God had mercy on David in this situation.
- God permitted some types of work, priestly work, on the Sabbath, and even Rabbinical law accepted saving someone's life as permitted on the Sabbath, thus medical work for saving a life would be allowed by their strict interpretation.
- Jesus states that He is greater than the Temple and Lord of the Sabbath, which only God can be. He is more capable of interpreting Sabbath law than the Pharisees.