In verse 23, the righteous followers of the Mosaic Law confront him about the habit of "plucking heads of grain" on the Sabbath. These Pharisees demand to know, "Why are they doing what is unlawful on the Sabbath?"
Mark's Jesus settles the conflict by employing three arguments. First, they're not the first Jews to break laws. He reminds the Pharisees that no one criticized King David and his men for eating forbidden sacrificial bread when they were running away from Saul. Then he adds as "Son of Man" he has power to do what he darn well pleases on the Sabbath.
It's his second argument that created problems for some early Christian communities and continues to do so today.
"The Sabbath," Jesus insists, "was made for man, not man for the Sabbath." In other words, God doesn't first create laws, and then create humans to obey them. God creates humans and then creates laws to help them live fulfilled lives.
Mark's Jesus is convinced that when a law does not help us achieve such fulfillment, we have no obligation to obey it. He expects his followers to judge every law and regulation on whether people are helped by it or hindered by it. No Christian is expected to obey a law just because it's a law.
Though this response definitively resolves this particular conflict with the Pharisees, it seems to have created another conflict in at least two other gospel communities.
Biblical scholars are convinced that Mark's Gospel is the first of our canonical four and that both Matthew and Luke had a copy when composing their own Gospels. Each generously copies from his evangelical predecessor. But each also "redacts" the material lifted from that manuscript — that is, they frequently alter Mark's passages to fit the theology they're trying to convey. And they do so independently. As far as we can tell, Matthew never read a copy of Luke and Luke doesn't seem to have known Matthew's Gospel existed.
Each of Mark's successors copies his Sabbath grain-plucking story almost exactly the way Mark originally penned it.
Matthew, for instance, writing for a Jewish/Christian audience, redacts Jesus' arguments by adding one about not criticizing temple priests for breaking the Mosaic Law by working on the Sabbath. But each deliberately leaves out Jesus' most cogent justification of his disciples' actions: his conviction that his followers aren't created to obey laws; laws are created to help people. People's welfare is always to be at the top of our moral hierarchy.
Why would Matthew and Luke deliberately leave out that statement?
Scholars usually come up with two reasons. First, the early Christian authors simply don't have the same passion for the actual words of Jesus. The evangelists are much more interested in what Jesus is saying during the day and age they're composing their Gospels than in what the historical Jesus said 40 or 50 years before.
The Jesus Christians encounter in the Gospels is no longer a first-century Palestinian Jew.
Second, this particular saying seems to be "too hot to handle" for many communities. How does one judge what laws and regulations are helpful and what are harmful? A law, for instance, that tears my family apart might offer great security to your family.
Luke and Matthew simply seem to have judged Jesus' most powerful argument in favor of lawbreaking unworkable in the concrete situations they and their communities encountered. They were convinced there'd always be someone who'd employ it for his or her selfish benefit instead of for the common good. So they concentrated on Jesus' other arguments, leaving out the one that created problems.