Josiah was eight years old when he became king, and he reigned in Jerusalem thirty-one years. He did what was right in the eyes of the LORD and walked in the ways of his father David, not turning aside to the right or to the left. In the eighth year of his reign, while he was still young, he began to seek the God of his father David. In his twelfth year he began to purge Judah and Jerusalem of high places, Asherah poles, carved idols and cast images. Under his direction the altars of the Baals were torn down; he cut to pieces the incense altars that were above them, and smashed the Asherah poles, the idols and the images. These he broke to pieces and scattered over the graves of those who had sacrificed to them. He burned the bones of the priests on their altars, and so he purged Judah and Jerusalem. In the towns of Manasseh, Ephraim and Simeon, as far as Naphtali, and in the ruins around them, he tore down the altars and the Asherah poles and crushed the idols to powder and cut to pieces all the incense altars throughout Israel. Then he went back to Jerusalem.

Josiah was twenty when he did that, and you could tell, he was serious. 'He burned the bones of the priests on their altars.' That sounds pretty serious.