Commentary on the Bible, by Adam Clarke, [1831], at sacred-texts.com
Jehoiada the priest, after having taken counsel with the captains, Levites, etc., proclaims Joash, and anoints him king, Ch2 23:1-11. Athaliah, endeavoring to prevent it, is slain, Ch2 23:12-15. He makes the people enter into a covenant, that they would serve the Lord, Ch2 23:16. The people break down the temple of Baal, and slay Mattan his priest, Ch2 23:17. Jehoiada makes several alterations, and remodels the kingdom, Ch2 23:18-21.
And in the seventh year - See on Kg2 11:4 (note), etc.
Spears and bucklers - See on Kg2 11:10 (note).
God save the king - May the king live! See on Kg2 11:12 (note).
And whoso followeth her, let him be slain with the sword - He who takes her part, or endeavors to prevent the present revolution, let him be immediately slain.
Of the horse-gate - See on Kg2 11:16 (note).
Made a covenant between him - The high priest was, on this occasion, the representative of God; whom both the people and the king must have had in view, through the medium of his priest.
Mattan the priest - The Targum will not prostitute the term priest, but calls him כומרא cumera, priestling.
The city was quiet - There was no attempt at a counter-revolution. Concerning the coronation of Joash, there is a curious circumstance mentioned by the Targumist on Ch2 23:11, it is as follows: - "And they brought forth the son of the king, and put on him the royal crown which David took from the head of the king of the children of Ammon. In it was inserted the precious attracting stone, in which was engraven and expressed the great and honorable Name [יהוה] which David had placed there by the Holy Spirit: and it was of the weight of a talent of gold; it was therefore a testimony to the house of David that no king who was not of the seed of David should be able to put it on his head, nor be able to bear its weight. When, therefore, the people saw it placed on the head of Joash, and that he was able to bear this crown, they believed him to be of the seed of David, and immediately constituted him king. Therefore Jehoiada and his sons anointed him, and said, May the king be prosperous in his kingdom!"
The Jews say that this was the crown of the king of the Ammonites; and that it was always worn afterwards by the kings of the house of Judah. See Jarchi on this place.