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 22:1
ch2 22:1AHAZIAH SUCCEEDING JEHORAM, REIGNS WICKEDLY. (Ch2 22:1-9)
the inhabitants of Jerusalem made Ahaziah . . . king--or Jehoahaz (Ch2 21:17). All his older brothers having been slaughtered by the Arab marauders, the throne of Judah rightfully belonged to him as the only legitimate heir.
2 Chronicles 22:2
ch2 22:2Forty and two years old was Ahaziah when he began to reign--(Compare Kg2 8:26). According to that passage, the commencement of his reign is dated in the twenty-second year of his age, and, according to this, in the forty-second year of the kingdom of his mother's family [LIGHTFOOT]. "If Ahaziah ascended the throne in the twenty-second year of his life, he must have been born in his father's nineteenth year. Hence, it may seem strange that he had older brothers; but in the East they marry early, and royal princes had, besides the wife of the first rank, usually concubines, as Jehoram had (Ch2 21:17); he might, therefore, in the nineteenth year of his age, very well have several sons" [KEIL] (compare Ch2 21:20; Kg2 8:17).
Athaliah the daughter of Omri--more properly, "granddaughter." The expression is used loosely, as the statement was made simply for the purpose of intimating that she belonged to that idolatrous race.
2 Chronicles 22:3
ch2 22:3his mother was his counsellor . . . they were his counsellors--The facile king surrendered himself wholly to the influence of his mother and her relatives. Athaliah and her son introduced a universal corruption of morals and made idolatry the religion of the court and the nation. By them he was induced not only to conform to the religion of the northern kingdom, but to join a new expedition against Ramoth-gilead (see Kg2 9:10).
2 Chronicles 22:5
ch2 22:5went . . . to war against Hazael, king of Syria--It may be mentioned as a very minute and therefore important confirmation of this part of the sacred history that the names of Jehu and Hazael, his contemporary, have both been found on Assyrian sculptures; and there is also a notice of Ithbaal, king of Sidon, who was the father of Jezebel.
2 Chronicles 22:6
ch2 22:6Azariah went down--that is, from Ramoth-gilead, to visit the king of Israel, who was lying ill of his wounds at Jezreel, and who had fled there on the alarm of Jehu's rebellion.
2 Chronicles 22:9
ch2 22:9he sought Ahaziah, and they caught him (for he was hid in Samaria)--(compare Kg2 9:27-29). The two accounts are easily reconciled. "Ahaziah fled first to the garden house and escaped to Samaria; but was here, where he had hid himself, taken by Jehu's men who pursued him, brought to Jehu, who was still near or in Jezreel, and at his command slain at the hill Gur, beside Ibleam, in his chariot; that is, mortally wounded with an arrow, so that he, again fleeing, expired at Megiddo" [KEIL]. Jehu left the corpse at the disposal of the king of Judah's attendants, who conveyed it to Jerusalem, and out of respect to his grandfather Jehoshaphat's memory, gave him an honorable interment in the tombs of the kings.
So the house of Ahaziah had no power to keep still the kingdom--His children were too young to assume the reins of government, and all the other royal princes had been massacred by Jehu (Ch2 22:8).
2 Chronicles 22:10
ch2 22:10ATHALIAH, DESTROYING THE SEED ROYAL SAVE JOASH, USURPS THE KINGDOM. (Ch2 22:10-12)
Athaliah . . . arose and destroyed all the seed royal--(See on Kg2 11:1-3). Maddened by the massacre of the royal family of Ahab, she resolved that the royal house of David should have the same fate. Knowing the commission which Jehu had received to extirpate the whole of Ahab's posterity, she expected that he would extend his sword to her. Anticipating his movements, she resolved, as her only defense and security, to usurp the throne and destroy "the seed royal," both because they were hostile to the PhÅnician worship of Baal, which she was determined to uphold, and because, if one of the young princes became king, his mother would supersede Athaliah in the dignity of queen mother.
2 Chronicles 22:12
ch2 22:12he was with them hid in the house of God--Certain persons connected with the priesthood had a right to occupy the buildings in the outer wall, and all within the outer wall was often called the temple. Jehoiada and his family resided in one of these apartments.