2 Chronicles 34:14
And when they brought out the money that was brought into the house of the LORD, Hilkiah the priest found a book of the law of the LORD given by Moses. And when they brought out the money that was brought into the house of the LORD, Hilkiah the priest found a book of the law of the LORD given by Moses.
During Josiah's reign, while the temple was being repaired and the money that had been brought into the house of the Lord was being brought out, Hilkiah the priest found the book of the law of the Lord given through Moses in the temple. The discovery took place in the course of the repair work ordered in his reign. The book was the temple copy of the law, including the covenant statutes recorded in Deuteronomy. It had been long lost through neglect during Manasseh's reign, leaving the people without its instruction for many years.
When its words were read and studied, they exposed Israel's departure from God's statutes and brought Scripture back to the people. That reading called them to repentance and reform. Josiah humbled himself, confessed his sin, and made a wholehearted covenant to keep the law, and the people also covenanted to obey, in a deep work of repentance and return to the Lord. That reformation temporarily averted threatened judgments. God's law still reveals transgression, and each person must repent and reform as its light reaches them, without compromising with evil. That reform illustrates the kind of response John expected his message from God to produce.