What does Mark 6:23 mean?

The promise of a ruler to give half of his kingdom is ancient and certainly hyperbolic. Although it is inferred in 1 Kings 13:8, the story of Esther gives the best examples. King Ahasuerus offers Esther half of his kingdom when she approaches him, when he has eaten her first banquet, and after he has eaten her second. She does not ask for half his kingdom, but she does ask that her people, the Jews, be able to defend themselves against those who would destroy them.

Most likely, neither the girl nor her mother expect Antipas to literally give them half his kingdom, but his impulsivity does give Herodias the chance she has been waiting for. The combination of his carelessness, his desire for the respect of his guests, and his most-likely-erotic response to his step-daughter's dancing will lead to the death of John the Baptist. This was an act Antipas had been avoiding in fear that John's disciples would rise against him (Matthew 14:5). If they rebel, Rome may decide he cannot rule properly, and give his position to another. In promising the girl half his kingdom, he winds up risking it all.

Instead of impulsive, God desires us to be steadfast. Not "children, tossed to and fro by the waves and carried about by every wind of doctrine, by human cunning, by craftiness in deceitful schemes" (Ephesians 4:14). He wants our faith to remain steady and not waffle in the face of persecution (Revelation 2:10). We are meant to seek the truth, not just what is pleasant to hear (2 Timothy 4:3), because "the one who endures to the end will be saved" (Mark 13:13).