What is the meaning of Mark 6:18?

For John had been telling Herod

John the Baptist spoke repeatedly, not just once. His steady voice was a conscience to Herod Antipas, just as prophets like Nathan confronted King David (2 Samuel 12:1-7) and Elijah challenged Ahab (1 Kings 18:17-18).

• Consistency: John “had been telling,” implying an ongoing call to repentance rather than a one-time rebuke.

• Courage: Like Peter and John later before the Sanhedrin (Acts 4:19-20), John feared God more than any earthly ruler.

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“It is not lawful

John appeals to God’s unchanging moral law, grounded in Scripture. Leviticus 18:16 and 20:21 clearly prohibit marrying a brother’s wife while he lives. Jesus will build on this same standard of lifelong marriage in Mark 10:6-9.

• Lawful means “in line with God’s revealed will,” not merely with human legality.

• By invoking the Law, John places Herod under the same authority every Israelite recognized, echoing Psalm 19:7: “The Law of the LORD is perfect.”

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for you to have your brother’s wife!”

Herod Antipas had divorced his own wife and taken Herodias, who was the wife of his still-living brother Philip (Josephus confirms this). John names the sin without softening it, much like Paul later confronts an immoral relationship in 1 Corinthians 5:1-2.

• Personal address: “for you” makes the rebuke direct and unavoidable.

• Specific sin: “to have” here points to an ongoing adulterous union, not a single lapse.

• Consequences: John’s bold declaration leads to his imprisonment (Mark 6:17) and, ultimately, martyrdom—reminding us of Jesus’ words in Matthew 5:10-12 about persecution for righteousness.

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summary

Mark 6:18 shows a faithful prophet applying God’s timeless Law to a powerful ruler’s public sin. John’s continual, scripturally grounded confrontation models how truth spoken with courage can expose wrongdoing, even when the cost is high.