2 Kings 12:1
In the seventh year of Jehu Jehoash began to reign; and forty years reigned he in Jerusalem. And his mother’s name was Zibiah of Beer-sheba. In the seventh year of Jehu Jehoash began to reign; and forty years reigned he in Jerusalem. And his mother’s name was Zibiah of Beer-sheba.
Jehoash is Joash, who began to reign in Jerusalem in the seventh year of Jehu when he was seven years old and reigned forty years there, and his mother was Zibiah of Beer-sheba. He was the true king of Judah who had been hidden in the temple from about a year old for six years until he was old enough to be proclaimed, after Athaliah usurped the kingdom and was then slain. His rise followed Athaliah carrying her mother Jezebel's spirit into Judah. It illustrates that Judah had good kings from time to time while the kings of Israel were invariably weak or altogether bad.
While under the instruction of Jehoiada the high priest he did what was right in the Lord's sight and remained faithful, with early inclinations favoring the kingdom's religious interests. He began a reform that destroyed Baal worship. His youth at first limited reform throughout the country, so the inclination to worship Baal continued and the priests were not properly provided for.
At about thirty years old he was regarded as mature with greater influence than when he first became king. He then determined to repair the temple that Athaliah had plundered, having money collected and given for repairing the house of God. In this he was a young repairer of the temple about two centuries before Josiah did a similar work. Afterward he repaid Jehoiada badly by having Jehoiada's sons killed.