A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
2 Chronicles 24:1
ch2 24:1JOASH REIGNS WELL ALL THE DAYS OF JEHOIADA. (Ch2 24:1-14)
Joash . . . began to reign--(See on Kg2 12:1-3).
2 Chronicles 24:3
ch2 24:3Jehoiada took for him two wives--As Jehoiada was now too old to contract such new alliances, the generality of interpreters apply this statement to the young king.
2 Chronicles 24:4
ch2 24:4Joash was minded to repair the house of the Lord--(See on Kg2 12:4-16).
2 Chronicles 24:15
ch2 24:15JEHOIADA BEING DEAD. (Ch2 24:15-16)
Jehoiada waxed old . . . and died--His life, protracted to unusual longevity and spent in the service of his country, deserved some tribute of public gratitude, and this was rendered in the posthumous honors that were bestowed on him. Among the Hebrews, intramural interment was prohibited in every city but Jerusalem, and there the exception was made only to the royal family and persons of eminent merit, on whom the distinction was conferred of being buried in the city of David, among the kings, as in the case of Jehoiada.
2 Chronicles 24:17
ch2 24:17JOASH FALLS INTO IDOLATRY. (Ch2 24:17-22)
Now came the princes of Judah, and make obeisance to the king--Hitherto, while Joash occupied the throne, his uncle had held the reins of sovereign power, and by his excellent counsels had directed the young king to such measures as were calculated to promote both the civil and religious interests of the country. The fervent piety, practical wisdom, and inflexible firmness of that sage counsellor exerted immense influence over all classes. But now that the helm of the state-ship was no longer steered by the sound head and firm hand of the venerable high priest, the real merits of Joash's administration appear; and for want of good and enlightened principle, as well as, perhaps, of natural energy of character, he allowed himself to be borne onward in a course which soon wrecked the vessel upon hidden rocks.
the king hearkened unto them, &c.--They were secretly attached to idolatry, and their elevated rank affords sad proof how extensively and deeply the nation had become corrupted during the reigns of Jehoram, Ahaziah, and Athaliah. With strong professions of allegiance they humbly requested that they might not be subjected to the continued necessity of frequent and expensive journeys to Jerusalem, but allowed the privilege their fathers had enjoyed of worshipping God in high places at home. They framed their petition in this plausible and least offensive manner, well knowing that, if excused attendance at the temple, they might--without risk of discovery or disturbance--indulge their tastes in the observance of any private rites they pleased. The weak-minded king granted their petition; and the consequence was, that when they left the house of the Lord God of their fathers, they soon "served groves and idols."
2 Chronicles 24:18
ch2 24:18wrath came upon Judah and Jerusalem--The particular mention of Jerusalem as involved in the sin implies that the neglect of the temple and the consequent idolatry received not only the king's toleration, but his sanction; and it naturally occurs to ask how, at his mature age, such a total abandonment of a place with which all his early recollections were associated can be accounted for. It has been suggested that what he had witnessed of the conduct of many of the priests in the careless performance of the worship, and especially their unwillingness to collect the money, as well as apply a portion of their revenues for the repairs of the temple, had alienated and disgusted him [LE CLERC].
2 Chronicles 24:19
ch2 24:19Yet he sent prophets--Elisha, Micah, Jehu son of Hanani, Jahaziel son of Zechariah (Ch2 20:14), Eliezer son of Dodavah (Ch2 20:37), lived and taught at that time. But all their prophetic warnings and denunciations were unheeded.
2 Chronicles 24:20
ch2 24:20the Spirit of God came upon Zechariah the son of Jehoiada--probably a younger son, for his name does not occur in the list of Aaron's successors (1Ch. 6:4-47).
stood above the people--Being of the priestly order, he spoke from the inner court, which was considerably higher than that of the people.
and said unto them, Thus saith God, Why transgress ye the commandments of the Lord, that ye cannot prosper, &c.--His near relationship to the king might have created a feeling of delicacy and reluctance to interfere; but at length he, too, was prompted by an irresistible impulse to protest against the prevailing impiety. The bold freedom and energy of [Zechariah's] remonstrance, as well as his denunciation of the national calamities that would certainly follow, were most unpalatable to the king; while they so roused the fierce passions of the multitude that a band of miscreants, at the secret instigation of Joash, stoned him to death. This deed of violence involved complicated criminality on the part of the king. It was a horrid outrage on a prophet of the Lord--base ingratitude to a family who had preserved his life--atrocious treatment of a true Hebrew patriot--an illegal and unrighteous exercise of his power and authority as a king.
2 Chronicles 24:22
ch2 24:22when he died, he said, The Lord look upon it and require it--These dying words, if they implied a vindictive imprecation, exhibit a striking contrast to the spirit of the first Christian martyr (Act 7:60). But, instead of being the expression of a personal wish, they might be the utterance of a prophetic doom.
2 Chronicles 24:23
ch2 24:23HE IS SLAIN BY HIS SERVANTS. (Ch2 24:23-27)
at the end of the year the host of Syria came up--This invasion took place under the personal conduct of Hazael, whom Joash, to save the miseries of a siege, prevailed on to withdraw his forces by a large present of gold (Kg2 12:18). Most probably, also, he promised the payment of an annual tribute, on the neglect or refusal of which the Syrians returned the following year, and with a mere handful of men inflicted a total and humiliating defeat on the collected force of the Hebrews.
2 Chronicles 24:25
ch2 24:25they left him in great diseases--The close of his life was embittered by a painful malady, which long confined him to bed.
his own servants conspired against him--These two conspirators (whose fathers were Jews, but their mothers aliens) were probably courtiers, who, having constant access to the bedchamber, could the more easily execute their design.
for the blood of the sons--read "the son" of Jehoiada. Public opinion seems to have ascribed the disasters of his life and reign to that foul crime. And as the king had long lost the esteem and respect of his subjects, neither horror nor sorrow was expressed for his miserable end!