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 23:1
ch2 23:1JEHOIADA MAKES JOASH KING. (Ch2 23:1-11)
in the seventh year Jehoiada . . . took the captains of hundreds, &c.--(See on Kg2 11:4; Kg2 11:17). The five officers mentioned here had been probably of the royal guard, and were known to be strongly disaffected to the government of Athaliah.
2 Chronicles 23:2
ch2 23:2chief of all the fathers of Israel--This name is frequently used in Chronicles for Judah and Benjamin, now all that remained of Israel. Having cautiously entrusted the secret of the young prince's preservation to all the leading men in the kingdom, he enlisted their interest in the royal cause and got their pledge to support it by a secret oath of fidelity.
they came to Jerusalem--The time chosen for the grand discovery was, probably, one of the annual festivals, when there was a general concourse of the nation at the capital.
2 Chronicles 23:4
ch2 23:4This is the thing that ye shall do--The arrangements made for defense are here described. The people were divided into three bodies; one attended as guards to the king, while the other two were posted at all the doors and gates, and the captains and military officers who entered the temple unarmed to lull suspicion, were furnished with weapons out of the sacred armory, where David had deposited his trophies of victory and which was reopened on this occasion.
2 Chronicles 23:8
ch2 23:8Jehoiada . . . dismissed not the courses--As it was necessary to have as large a disposable force as he could command on such a crisis, the high priest detained those who, in other circumstances, would have returned home on the expiry of their week of service.
2 Chronicles 23:11
ch2 23:11Then they brought out the king's son, and put upon him the crown, and gave him the testimony--Some think that the original word rendered "testimony," as its derivation warrants, may signify here the regalia, especially the bracelet (Sa2 1:10); and this view they support on the ground that "gave him" being supplemented, the text properly runs thus, "put upon him the crown and testimony." At the same time, it seems equally pertinent to take "the testimony" in the usual acceptation of that term; and, accordingly, many are of opinion that a roll containing a copy of the law (Deu 17:18) was placed in the king's hands, which he held as a scepter or truncheon. Others, referring to a custom of Oriental people, who when receiving a letter or document from a highly respected quarter, lift it up to their heads before opening it, consider that Joash, besides the crown, had the book of the law laid upon his head (see Job 31:35-36).
God save the king--literally, "Long live the king."
2 Chronicles 23:12
ch2 23:12ATHALIAH SLAIN. (Ch2 23:12-15)
Athaliah heard the noise of the people--The unusual commotion, indicated by the blast of the trumpets and the vehement acclamations of the people, drew her attention, or excited her fears. She might have flattered herself that, having slain all the royal family, she was in perfect security; but it is just as likely that, finding on reflection, one had escaped her murderous hands, she might not deem it expedient to institute any enquiries; but the very idea would keep her constantly in a state of jealous suspicion and irritation. In that state of mind, the wicked usurper, hearing across the TyropÅon the outburst of popular joy, rushed across the bridge to the temple grounds, and, penetrating from a single glance the meaning of the whole scene, raised a shriek of "Treason!"
2 Chronicles 23:13
ch2 23:13behold, the king stood at his pillar at the entering in--The king's pillar was in the people's court, opposite that of the priests'. The young king, arrayed in the royal insignia, had been brought out of the inner, to stand forth in the outer court, to the public view. Some think that he stood on the brazen scaffold of Solomon, erected beside the pillar [see on Ch2 6:13].
2 Chronicles 23:14
ch2 23:14Slay her not in the house of the Lord . . . and when she was come to the entering of the horse gate by the king's house, they slew her there--The high priest ordered her immediately to be taken out of the temple grounds and put to death. "And they laid hands on her; and she went by the way by the which horses came into the king's house: and there was she slain" (Kg2 11:16). "Now, we are not to suppose that horses came into [the king's house] of residence, but into the king's (horses') house or hippodrome (the gate of the king's mules) [JOSEPHUS], he had built for them on the southeast of the temple, in the immediate vicinity of the horse gate in the valley of Kedron--a valley which was at that time a kind of desecrated place by the destruction of idols and their appurtenances" (Kg2 23:2, Kg2 23:6, Kg2 23:12) [BARCLAY, City of the Great King].
2 Chronicles 23:16
ch2 23:16JEHOIADA RESTORES THE WORSHIP OF GOD, AND SETTLES THE KING. (Ch2 23:16)
Jehoiada made a covenant--(See on Kg2 11:17).