What David did...

Matthew 12:3-4 "Have you not read what David did ... entered the house of God, and they ate the consecrated bread, which was not lawful for him to eat..." It seemed an odd reference--to history rather than the law, and to an incident in which David, on the run from Saul, lies to Ahimelech the priest at the tabernacle about his errand. That's a pretty odd precedent to rely on.

I think I get it now, though. Ahimelech gave him permission, and Jesus was affirming that. Jesus' next example is also about the priests in the temple, who do work (and hard work it was) on the Sabbath--unlike everybody else. Jesus then claims to be superior to the temple, which the priests serve, so if a priest can intepret, even more He can specify the applications of the law.