Jesus answered them, “Have you never read what David did when he and his companions were hungry? He entered the house of God, and taking the consecrated bread, he ate what is lawful only for priests to eat. And he also gave some to his companions.” Luke 6:3-4
The Pharisees were aware of this Mosaic law, “If you enter your neighbor’s vineyard, you may eat all the grapes you want, but do not put any in your basket. If you enter your neighbor’s grainfield, you may pick kernels with your hands, but you must not put a sickle to their standing grain” (Deuteronomy 23:24-25). But the Pharisees had added extra requirements to the law. So when they saw the disciples picking grain, rubbing it in their hands and eating the kernels, they accused them of working on the Sabbath.
Jesus decides that rather than explain the error of the Pharisees’ traditions, he makes the more telling point that human need takes precedence over ceremonial law and the observance of rituals. Jesus draws their attention to the time when David and his companions ate consecrated bread (1 Samuel 21:1-6).
What David did was broke the ceremonial laws (Leviticus 24:9) but he wasn’t rebuked for it. Later when he broke God’s moral law there were dire consequences (2 Samuel 12:18). The ceremonial laws told Israel how to worship God. The moral laws told Israel how to live. David understood this. He knew God’s heart. It wasn’t outward conformity to a set of rules that pleases God but rather a heart desire to please God.
David understood God’s purposes in giving the law, something the Pharisees consistently failed to do. Likewise, God wants us to understand his purposes and therefore what pleases him.