The book — That original book of the law of the Lord, given or written by the hand of Moses, as it is expressed, 2 Chronicles 34:14, which by God's command was put beside the ark, Deuteronomy 31:26, and probably taken from thence and hid, by the care of some godly priest, when some of the idolatrous kings of Judah persecuted the true religion, and defaced the temple, and (which the Jewish writers affirm) burnt all the copies of God's law which they could find. It was now found among the rubbish, or in some secret place.
Related Commentaries of 2 Kings 22:8
2 Kings 22:8
8 And Hilkiah the high priest said unto Shaphan the scribe, I have found the book of the law in the house of the LORD. And Hilkiah gave the book to Shaphan, and he read it.