What does Luke 6:2 mean?

This is the second of five conflicts Jesus faces while choosing His disciples. In the first, Pharisees and scribes silently judged Him for claiming that a man's sins were forgiven (Luke 5:21). When Jesus chose Matthew to be a disciple, they criticized Jesus for eating with tax collectors and sinners (Luke 5:30). Then, John the Baptist's disciples questioned Jesus for not encouraging His disciples to fast (Luke 5:33). After this, scribes and Pharisees will lie in wait to see if Jesus will heal a man on the Sabbath. He does (Luke 6:6–11).

"Lawful" means "right," or "proper," or "authorized." The Pharisees claimed to greatly revere the law of the Jews. In addition to the Mosaic law, they followed and enforced the oral law, which scribes claimed God gave to Moses but didn't tell him to write down. The oral law supposedly includes specific applications of how to follow the Mosaic law. Pharisees believed the oral law was as binding as the Mosaic law. The Mosaic law forbids Jews from working on the Sabbath (Exodus 31:14–15) but doesn't strictly define what "work" is.

The oral law includes harvesting grain and separating the kernel from the chaff as "work." Certainly, God did not intend the Israelites to harvest their fields on the Sabbath. However, Jesus points out that preventing a hungry man from plucking heads of grain as he walks through a field is contrary to God's gift of the Sabbath as a blessing (Mark 2:27).