What does Mark 12:4 mean?

Jesus is using a story to compare the Jewish religious and civil leaders to rebellious farm tenants and the Old Testament prophets to the vineyard owner's servants. Like many of Israel's kings, the religious and civil leaders of Jesus' day forget that God is the true leader of their nation.

Being a prophet was a dangerous job. In the course of their duties, Zechariah was stoned (2 Chronicles 24:20–22) and Uriah was struck by a sword (Jeremiah 26:20–23). Daniel, of course, was thrown into a lions' den (Daniel 6), and Jonah was commanded to preach repentance to the vile, violent Ninevites (Jonah 1:1–2). When Jesus speaks the words recorded here, John the Baptist has been beheaded, and Jesus is days from the crucifixion. Unlike the servants in the allegory, some prophets did bring the fruit of people's hearts to their Master, but they payed dearly for it.

"Shamefully" is from the Greek root word atimazō, meaning "to treat contemptuously, to dishonor." It is also used to describe the treatment the high priest and the Sadducees give the apostles (Acts 5:17–42). The apostles are released after a mock trial, but as they leave, they have an interesting reaction. They praise God that "they were counted worthy to suffer dishonor" for Christ (Acts 5:41).

In the modern day, believers often demand others respect our "rights" as Christians. That's not a bad thing to do, at all (Acts 22:25–29). But we less frequently stop to praise God for what persecution proves: that we are following Him diligently enough to draw the attention of an evil world. Paul tells Timothy, "Indeed, all who desire to live a godly life in Christ Jesus will be persecuted" (2 Timothy 3:12). When life within a godless, secular culture is easy, uncontroversial, and serene, we should at least question how much the world sees God in us.