Would have killed - Εζητει, Sought to kill him. C and five of the Itala.

See the whole of this account, from Mark 6:17-29, explained on Matthew 14:2-12 (note).

Therefore Herodias had a quarrel against him,.... Was angry with him, conceived wrath, and laid up hatred against him, and was an adversary to him; which is the sense of the Oriental versions. She bore him an inward grudge, and lay in wait to take the first opportunity of dispatching him:

and would have killed him, but she could not; being hindered by Herod, who as yet would not suffer it; partly through fear of the people, and partly through the respect he had for John.

Had a quarrel against him (ἐνεῖχεν αὐτῷ)

There is some dispute about the rendering. The Rev. renders Set herself against him, with no alternative translation in the margin; and in Luke 11:53, Press upon him vehemently, with set themselves against him in the margin. I see no objection to rendering was angry at him, taking ἐνεῖχεν αὐτῷ with an ellipsis of χόλον, anger. Very literally, had within herself (ἐν) anger against him. So Herodotus, 1:118. Astyages concealing the anger (τόν χόλον) which he felt toward him (οἱ ἐνεῖχε). 6:119, ἐνεῖχε σφῖ δεινὸν χόλον, nourished a fierce anger against them. So Moulton, Grimm, and De Wette.

Desired (ἤθελεν)

Imperfect tense, was desiring all along. Her demand for John's murder was the result of a long-cherished wish.

Therefore Herodias {m} had a quarrel against him, and would have killed him; but she could not:

(m) Sought all means to hurt him.

6:19 Would have killed him. The wicked woman sought his murder, but could not kill him because Herod refused to consent.

a quarrel: or, an inward grudge

19. Therefore Herodias had a quarrel against him-rather, as in the Margin, "had a grudge against him." Probably she was too proud to speak to him; still less would she quarrel with him.

and would have killed him; but she could not.

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.