Mark 6:18
For John had been saying to Herod, it is not lawful for you to have your brother's wife — John's prophetic confrontation of the king follows the pattern of Elijah's confrontation of Ahab (1 Kings 18, 21) — the prophet who speaks the uncomfortable truth to the powerful, regardless of personal consequences. The is not lawful is a Torah legal declaration, not merely a moral opinion: John is applying Leviticus 20:21 to Herod's specific situation. This is the prophetic role — applying the word of God to the specific situations of specific people in power, regardless of their power.