The Geneva Bible Translation Notes, [1599], at sacred-texts.com
(a) The Scripture calls them sons who are either children or nephews.
Look even out the best and meetest of your master's sons, and (b) set [him] on his father's throne, and fight for your master's house.
(b) He wrote this, to prove them whether they would take his side or not.
Then he wrote a letter the second time to them, saying, If ye [be] mine, and [if] ye will hearken unto my voice, (c) take ye the heads of the men your master's sons, and come to me to Jezreel by to morrow this time. Now the king's sons, [being] seventy persons, [were] with the great men of the city, which brought them up.
(c) God as a just judge punishes the wicked children of wicked parents to the third and fourth generations.
And it came to pass in the morning, that he went out, and stood, and said to all the people, Ye [be] (d) righteous: behold, I conspired against my master, and slew him: but who slew all these?
(d) You cannot justly condemn me for the king's death, seeing as you have done the same to his posterity: for the Lord commanded me, and moved you to carry out his judgment.
So Jehu slew all that remained of the house of Ahab in Jezreel, and all his great men, and his kinsfolks, and his (e) priests, until he left him none remaining.
(e) Meaning, the idolatrous priests.
And he said, Take them alive. And they took them alive, and slew them at the pit of the shearing house, [even] two and forty men; (f) neither left he any of them.
(f) Thus God's vengeance is on them who have any part or familiarity with the wicked.
And when he was departed thence, he lighted on Jehonadab the son of Rechab [coming] to meet him: and he (g) saluted him, and said to him, Is thine heart right, as my heart [is] with thy heart? And Jehonadab answered, It is. If it be, give [me] thine hand. And he gave [him] his hand; and he took him up to him into the chariot.
(g) For he feared God, and lamented the wickedness of those times: therefore Jehu was glad to join with him: of Rechab read (Jer 35:2).
And Jehu gathered all the people together, and said unto them, Ahab served (h) Baal a little; [but] Jehu shall serve him much.
(h) Here Baal is taken for Ashtaroth the idol of the Zidonians, who Jezebel caused to be worshipped, as it is also so used in (Kg1 22:53).
And Jehu went, and Jehonadab the son of Rechab, into the house of Baal, and said unto the worshippers of Baal, Search, and look that there be here with you none of the (i) servants of the LORD, but the worshippers of Baal only.
(i) Thus God would have his servants preserved and idolaters destroyed, as in his law he gives express command, (Deu 13:5).
And it came to pass, as soon as he had made an end of offering the burnt offering, that Jehu said to the guard and to the captains, Go in, [and] slay them; let none come forth. And they smote them with the edge of the sword; and the guard and the captains cast [them] out, and went to the (k) city of the house of Baal.
(k) Which was near Samaria.
And the LORD said unto Jehu, Because thou hast done well in executing [that which is] right in mine eyes, [and] hast done unto the house of Ahab according to all that [was] in mine heart, thy (l) children of the fourth [generation] shall sit on the throne of Israel.
(l) Thus God approves and rewards his zeal, in executing God's judgment, though his wickedness was later punished.