What does Mark 6:24 mean?

Herod Antipas has imprisoned John the Baptist to keep him safe from Herodias, who wishes to kill him. John has publicly chastened Antipas for marrying his living brother's wife. Antipas feels both intrigued and uncomfortable about the message, but he hesitates to kill John for fear John's followers will rise up and rebel. His borders are already vulnerable thanks to his divorce from the daughter of the Nabatean king. If Nabatea invades at the same moment the Jews rebel, he could lose everything.

Herodias has the same ultimate concern, but she isn't as far-sighted as Antipas. She had divorced her husband, a prominent Roman citizen and Antipas' half-brother, and forced Antipas to divorce the Nabatean princess. Although Antipas isn't legitimately a king, in this overlooked and occupied territory, Herodias can pretend thanks to the Roman government who put him in power. Herodias, on her part, seems to believe that John and John alone is the threat. His message is disrespectful to her position as queen. She cares little for John's correct accusation that she's breaking Jewish laws of incest; she seems only to cares about her crown and reputation. To this end, Herodias has been trying to kill John the Baptist for a while. This impulsive promise Antipas gives her daughter provides the opportunity she has been waiting for.

Beheading was a manner of death used to demonstrate dominance, as well as confirm the victim's death. David cut off the head of Goliath to show he was dead (1 Samuel 17:51). The Old Testament offers other examples, generally during times of warfare (1 Samuel 31:9; 2 Samuel 4:7; 20:22; 2 Kings 10:6–8). In Acts 12:2, James the apostle is "killed … with the sword," likely indicating a beheading. This brutal form of execution is less violent and quicker than crucifixion, and the Romans often used it when they needed to end a life quickly, relatively humanely, and with incontrovertible proof.