Commentary on the Bible, by Adam Clarke, [1831], at sacred-texts.com
Ahaziah beans to reign; and reigns wickedly under the counsels of his bad mother, Ch2 22:1-4. He is slain by Jehu, who destroys all the house of Ahab, Ch2 22:5-9. Athaliah destroys all the seed royal of Judah, except Joash, who is hidden by his nurse in the temple six years, Ch2 22:10-12.
Made Ahaziah his youngest son king - All the others had been slain by the Arabians, etc.; see the preceding chapter, Ch2 21:17 (note).
Forty and two years old was Ahaziah - See the note on Kg2 8:26. Ahaziah might have been twenty-two years old, according to Kg2 8:26 (note), but he could not have been forty-two, as stated here, without being two years older than his own father! See the note there. The Syriac and Arabic have twenty-two, and the Septuagint, in some copies, twenty. And it is very probable that the Hebrew text read so originally; for when numbers were expressed by single letters, it was easy to mistake מ mem, Forty, for כ caph, Twenty. And if this book was written by a scribe who used the ancient Hebrew letters, now called the Samaritan, the mistake was still more easy and probable, as the difference between caph and mem is very small, and can in many instances be discerned only by an accustomed eye.
The reading in Kg2 8:26 is right, and any attempt to reconcile this in Chronicles with that is equally futile and absurd. Both readings cannot be true; is that therefore likely to be genuine that makes the son two years older than the father who begat him? Apage hae nugae!
His mother was his counsellor - Athaliah, the wicked daughter of a wicked parent, and the wicked spouse of an unprincipled king.
Went with Jehoram - See on Kg2 8:28 (note).
He sought Ahaziah - See a different account Kg2 9:27 (note), and the note there, where the accounts are reconciled.
All the seed royal of the house of Judah - Nothing but the miraculous intervention of the Divine providence could have saved the line of David at this time, and preserved the prophecy relative to the Messiah. The whole truth of that prophecy, and the salvation of the world, appeared to be now suspended on the brittle thread of the life of an infant of a year old, (see Ch2 24:1), to destroy whom was the interest of the reigning power! But God can save by few as well as by many. He had purposed, and vain were the counter-exertions of earth and hell.
Hid in the house of God - "In the house of the sanctuary of God." - Targum. Or, as he says on Ch2 22:11, בקודש קודשיא bekudash kudeshaiya "in the holy of holies." To this place Athaliah had no access, therefore Joash lay concealed, he and his affectionate aunt-nurse. - See on Kg2 11:1 (note).