See this account of the death of John the Baptist fully explained in the notes at Matthew 14:1-12.

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.

And king Herod heard of him,.... "Of Jesus", as the Syriac version supplies it; or "the miracles of Jesus", as the Persic version. This Herod here called a king, as he might be by his courtiers, and the common people, is the same with the Tetrarch in Matthew 14:1, for he was only Tetrarch of Galilee. This was Herod Antipater, the son of Herod the Great; the fame of Jesus reached his ears, he being governor of those parts, which were mostly visited by Christ:

for his name was spread abroad; by means of his ministry and miracles, and through those of his disciples, whom he had sent two by two into all parts of the country:

and he said that John the Baptist was risen from the dead, and therefore mighty works do show forth themselves in him; for Herod had some time before put John to death; and hearing of these wonderful things that were done by Christ, his conscience smote him for the murder of John; and such a thought struck into his mind, that he was risen from the dead, and did these miracles: and the more he thought of it, the more strongly he was persuaded of it; and told it to his courtiers with a great deal of assurance, that it was certainly he; See Gill on Matthew 14:2.

Was spread abroad

"But for the rumor, Herod would not have known of him. A palace is late in hearing spiritual news" (Bengel).

Mighty works do show forth themselves in him (ἐνεργοῦσιν αἱ δυνάμεις ἐν αὐτῷ)

Rev., these powers work in him. As Dr. Morison observes, "A snatch of Herod's theology and philosophy." He knew that John wrought no miracles when alive, but he thought that death had put him into connection with the unseen world, and enabled him to wield its powers.

{5} And king Herod heard of him; (for his name was spread abroad:) and he said, That John the Baptist was risen from the dead, and therefore mighty {i} works do shew forth themselves in him.

(5) The gospel confirms the godly and vexes the wicked.

(i) The word signifies powers, by which is meant the power of working miracles.

6:14 And king Herod heard of him. For Herod's opinion of Christ and the death of John the Baptist, see notes on Mt 14:1-12. Compare Lu 9:7-9.

6:14 Mt 14:1; Lu 9:7.

Margin Herod

Son of the Herod of our Lord's nativity; also vs. Mk 1:16-18,20-22 See margin ref., Mt 14:1 See Scofield Note: "Mt 14:1"

Mr 6:14-29. Herod Thinks Jesus a Resurrection of the Murdered Baptist-Account of His Death. ( = Mt 14:1-12; Lu 9:7-9).

Herod's View of Christ (Mr 6:14-16).

14. And King Herod-that is, Herod Antipas, one of the three sons of Herod the Great, and own brother of Archelaus (Mt 2:22), who ruled as ethnarch over Galilee and Perea.

heard of him; (for his name was spread abroad); and he said-"unto his servants" (Mt 14:2), his councillors or court ministers.

That John the Baptist was risen from the dead-The murdered prophet haunted his guilty breast like a specter, and seemed to him alive again and clothed with unearthly powers, in the person of Jesus.

6:14-29 Herod feared John while he lived, and feared him still more when he was dead. Herod did many of those things which John in his preaching taught him; but it is not enough to do many things, we must have respect to all the commandments. Herod respected John, till he touched him in his Herodias. Thus many love good preaching, if it keep far away from their beloved sin. But it is better that sinners persecute ministers now for faithfulness, than curse them eternally for unfaithfulness. The ways of God are unsearchable; but we may be sure he never can be at a loss to repay his servants for what they endure or lose for his sake. Death could not come so as to surprise this holy man; and the triumph of the wicked was short.