Mark 6:17

“For Herod himself had sent forth, etc..] Some of his guard, a detachment of soldiers, and laid hold upon John; who seized upon him, and took him up: and bound him in prison; in the castle of Machaerus: for Herodias' sake, his brother Philip's wife, for he had married her; whilst his brother was living, and who had had children by her; (see Gill on “<401403>Matthew 14:3”).”

“See this account of the death of John the Baptist fully explained in the notes at Matthew 14:1-12. Mark 6:20 For Herod feared John - That is, he stood in awe of him on account of his sanctity, and his boldness and fearlessness in reproving sin. Knowing that he was a just man and an Holy - A holy, pious, upright, honest man - a man who would not be afraid of him, or afraid to speak his real sentiments. And observed him - Margin, “kept him, or saved him.” This does not mean that he “observed” or obeyed his teachings, but that he kept him in safe custody in order to preserve him from the machinations of Herodias. He was willing to show his respect for John, and to secure him from danger, and…”

“6:17 imprison John: The Jewish historian Josephus (Antiquities 18.5.2) says that John was imprisoned in the fortress of Machaerus in Perea. • Josephus (Antiquities 18.5.1–4) states that Herodias was the wife of Herod Antipas’s half brother, Herod Philip.”

“am 4032, ad 28 Herod: Mat 4:12, Mat 11:2, Mat 14:3-12; Luk 3:19, Luk 3:20 Philip's: Luk 3:1 Mark 6:18”