John Gill's Bible Commentary Ver. 1. In the second year of Joash son of Jehoahaz king of Israel reigned Amaziah the son of Joash king of Judah .] As Joash king of Israel began to reign in the thirty seventh of Joash king of Judah, ( 2 Kings 13:10), who reigned forty years, Amaziah must therefore begin his reign in the fourth of Joash king of Israel; this therefore must be understood of his second year after he reigned alone, for he reigned two or three years in his father’s lifetime.
Matthew Henry Commentary
Verses 1-7 - Amaziah began well, but did not go on so. It is not enough to do tha which our pious predecessors did, merely to keep up the common usage but we must do it as they did, from the same principle of faith an devotion, and with the same sincerity and resolution.
Original Hebrew בשׁנת8141 שׁתים8147 ליואשׁ3101 בן1121 יואחז3099 מלך4428 ישׂראל3478 מלך4427 אמציהו558 בן1121 יואשׁ3101 מלך4428 יהודה׃3063