It was his own servants who slew wicked King Amon. His eight year old son, Josiah, was then placed on the throne of Judah. It is recorded in 2 Kings 22:2 that "he did that which was right in the sight of the LORD, and walked in all the way of David his father, and turned not aside to the right hand or to the left."
Josiah was a young man when, as repair of the house of the LORD was underway, the High Priest found there the book of the law (verse 8).
This book contained not only the law, but the blessings of obedience and the consequences for disobedience to the law. It took just one reading of the book for Josiah to realize that Judah was deserving of dire consequences for their rebellion against God. Josiah "rent his clothes, and the king commanded . . . saying, Go ye, inquire of the LORD . . . concerning the words of this book that is found: for great is the wrath of the LORD that is kindled against us, because our fathers have not hearkened unto the words of this book, to do according unto all that which is written concerning us" verses 11-13.
The message from the LORD, received from the prophetess Huldah, was that Judah would surely be punished, but that it would not be in Josiah's lifetime. Consider Josiah's options at that point. To pursue more reforms would be an all uphill effort and Judah was going to experience the wrath of God anyway, so why bother? But praise the LORD that Josiah thought differently. He threw himself into revival and reformation such as Judah had not before experienced. God's will was ever before him. "And the king . . . made a covenant before the LORD, to walk after the LORD, and to keep his commandments and his testimonies and his statutes with all their heart and all their soul, to perform the words of this covenant that were written in this book. And all the people stood to the covenant" 2 Kings 23:3. He then proceeded to rid the country of all that had to do with idol worship, and a thorough work he did! (See 2 Kings 23). This was a man who cared deeply for his people. He was determined to do whatever he could for their salvation. Would we be willing to extend ourselves for others as he did?
"And like unto him was there no king before him, that turned to the LORD with all his heart, and with all his soul, and with all his might, according to all the law of Moses; neither after him arose there any like him (verse 25).