What does Mark 2:16 mean?The scribes are a subset of Pharisees. After the Jews returned to Israel from Babylon, the people resolved to follow and obey God like never before. The scribes developed rules that acted like a buffer around the Mosaic Law. For example, to protect people from breaking the Sabbath, they enacted thirty-nine new laws that very specifically explained what breaking the Sabbath entailed—in their opinion—and how to avoid it.
The scribes also deeply respect the dietary laws. No fewer than four sections in the Mishnah warn against eating with someone "of the land," which is another term for a Jew who does not follow these extra-biblical laws. Pharisees tithe on even the tiniest of foodstuffs (Matthew 23:23), and are meticulous about making sure they are ceremonially clean before they eat (Mark 7:3–4). To eat with "sinners" means to risk eating with someone who has not properly tithed on his food and who might not be ceremonially clean. This is absolutely unacceptable to them.
The root of the word "Pharisee" is the Greek parash which means "to make distinct or to separate." The Pharisees excel at separating themselves from the general populace. By questioning Jesus' disciples, the scribes reveal that they consider Jesus to be like a Pharisee—a teacher of the Law—if somewhat of a wild-card. They expect Jesus to live like they do because they initially assume He will think and teach the same way they do. When He breaks their rules, they become distressed that a self-labelled teacher could have so little regard for their customs.
Jesus will directly address the scribes' concerns about meals and traditions in Mark 7:1–23. Jesus says, "There is nothing outside a person that by going into him can defile him, but the things that come out of a person are what defile him" (Mark 7:15). Tithing or not, washing hands or not, eating with religious leaders or with tax-collectors—even eating non-kosher foods (Acts 10:9–16)—no broken tradition or even law can make someone unclean as much as a heart hardened against God and His people.