What does Mark 2:28 mean?

Mark 2:27–28 are not necessarily direct, word-for-word quotes from Jesus. Instead, they are probably Mark's summary of the event. The belief that the account is a summary and not a full transcript is supported by the extra narrative found in Matthew 12:1–8. Jesus is wrapping up a defense of His disciples for picking and eating grain on the Sabbath. His overall point is that Sabbath laws were meant for the benefit of the people, not as a burden. Nit-picking and overly literal obedience is not meant to override the real purpose of such laws.

The Pharisees have serious objections with Jesus' statement here. He again refers to Himself as "the Son of Man," which is from Daniel's description of the Messiah (Daniel 7:13). It is inconceivable to the Pharisees that this man is the promised savior of Israel. They believe the Messiah will be a man, a great man, but not one who takes such initiative as to forgive another's sins (Mark 2:5–7), socialize with sinners (Mark 2:13–17), disagree with religious leaders on fasting (Mark 2:18–22), or—especially—to endorse what they see as disrespect of the Sabbath.

The phrase "lord even of the Sabbath" is yet more heretical to Pharisaical ears. God established the Sabbath. No man can take authority over God's law. The Pharisees understand that Jesus is declaring He is God. These blasphemous remarks put the Pharisees on the look-out. In the fifth of the five stories of Jesus asserting His authority (Mark 3:1–6), the Pharisees actively watch Jesus to see if He will express such things again. When He does, they decide it is time to seek out His death.