And king Herod heard? - Την ακοην αοτου, his fame, is added by KM, fifteen others, and in the margin of several. It seems necessary to complete the sense.
See this account of the death of John the Baptist fully explained in the notes at Matthew 14:1-12.
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 even to do “many things” which might indicate respect for him - at least, to do so much as to guard him from his enemies.
And did many things - But he did not do the thing which was demanded of him - to break off from his sins. He attempted to make a compromise with his conscience. He still loved his sins, and did “other” things which he supposed might be accepted in the place of putting away, as he ought, the wife of his brother - the polluted and adulterous woman with whom he lived. Perhaps he treated John kindly, or spoke well of him, or aided him in his wants, and attempted in this way to silence his rebukes and destroy his faithfulness. This was probably before John was imprisoned. So sinners often treat ministers kindly, and do much to make them comfortable, and hear them gladly, while they are still unwilling to do the thing which is demanded of them - to repent and believe the gospel. They expect that their kind attentions will be accepted in the place of what God demands - repentance and the forsaking of their sins.