The Pharisees were fuming. Jesus' disciples had plucked grain on the Sabbath. But Jesus had an ace up his sleeve: David, a man after God's own heart, had done something even more 'illegal'.
Jesus points to King David's desperate act as a precedent for his disciples' actions.
David's Hunger, David's Choice
When David was fleeing from Saul, he and his men were starving. They went to the tabernacle, and David asked the priest for food. The only thing available was the 'bread of the Presence' (also called the 'showbread'). This bread was sacred, meant only for the priests to eat. It was a symbol of God's continuous presence with His people.
The Law and the Exception
The Law of Moses was very clear: only priests could eat this bread. It wasn't lawful for ordinary people, let alone for them to eat it on the Sabbath! Yet, the priest Ahimelech gave it to David and his men, and they ate it.
Jesus' Point
Jesus isn't saying the Law was wrong. He's showing that when a life-or-death need arises, God's mercy and the preservation of life can take precedence over strict ritual observance. God desires 'mercy, not sacrifice.'