Jesus gives a three part defense for the action of his disciples: The first is an example, the second is a precept, and the third is an a fortiori argument.
First, he gives an EXAMPLE. David broke the ritual laws it in the OT (1 Sam. 21).
Second, the priests were commanded to do it as a PRECEPT. In the OT, the priests needed to offer a sacrifice on the Sabbath (Num. 28:9-10) and offer the consecrated bread on the Sabbath (Lev. 24). This was work, but it was permitted for God’s purposes.
Third, Jesus uses an A FORTIORI argument to clinch his argument. The Temple was God’s presence in part, but Jesus was God’s presence in full. Therefore, if priests could “break” the Sabbath based on God’s orders in the Temple, then the disciples could “break” them for the greater Temple (v.6).
“But when the Pharisees saw it, they said unto him, Behold, thy disciples do that which is not lawful to do upon the sabbath day. But he said unto them, Have ye not read what David did, when he was an hungred, and they that were with him; How he entered into the house of God, and did eat the shewbread, which was not lawful for him to eat, neither for them which were with him, but only for the priests? Or have ye not read in the law, how that on the sabbath days the priests in the temple profane the sabbath, and are blameless? (Matt 12:2-5)”
