The future didn't just look gloomy. God promised it would be so. The king's response to this certain future revealed the true substance of his heart.

King Josiah
Since becoming king of Judah at age eight (2 Chronicles 34), Josiah had always been "God-haunted." Because Judah had so abandoned God, he had no specific, special, written revelation of God. Still, this "God-haunted-ness" had led Josiah to destroy false idols and altars and to rebuild the temple.

The high priest over the re-construction discovered something that would both solidify Josiah's devotion to the LORD and reveal a dismal future for Judah.

While they were bringing out the money that had been brought into the house of the LORD, Hilkiah the priest found the Book of the Law of the LORD given through Moses. Then Hilkiah answered and said to Shaphan the secretary, “I have found the Book of the Law in the house of the LORD.” And Hilkiah gave the book to Shaphan. Shaphan brought the book to the king, and further reported to the king, “All that was committed to your servants they are doing. They have emptied out the money that was found in the house of the LORD and have given it into the hand of the overseers and the workmen.” Then Shaphan the secretary told the king, “Hilkiah the priest has given me a book.” And Shaphan read from it before the king.

And when the king heard the words of the Law, he tore his clothes. (2 Chronicles 34.14–19)

Josiah's first response was grief for how far Judah had fallen. It is important to note that he had no knowledge yet of the results of this disobedience. His grief is simply about the separation between Judah and God. After tearing his clothes in grief, he looks to God for direction about the future.

“Go, inquire of the LORD for me and for those who are left in Israel and in Judah, concerning the words of the book that has been found. For great is the wrath of the LORD that is poured out on us, because our fathers have not kept the word of the LORD, to do according to all that is written in this book.” (2 Chronicles 34.21)

God would bring a promised punishment. It would be devastating to Judah. Not maybe. Definitely. Josiah himself would not see this devastation. He would die in peace. But the future is set. God promised it.

Thus says the LORD, Behold, I will bring disaster upon this place and upon its inhabitants, all the curses that are written in the book that was read before the king of Judah. Because they have forsaken me and have made offerings to other gods, that they might provoke me to anger with all the works of their hands, therefore my wrath will be poured out on this place and will not be quenched. (2 Chronicles 34.24–25)

you have humbled yourself before me and have torn your clothes and wept before me, I also have heard you, declares the LORD. Behold, I will gather you to your fathers, and you shall be gathered to your grave in peace, and your eyes shall not see all the disaster that I will bring upon this place and its inhabitants.’ (2 Chronicles 34.27–28)

What happens next is important
Josiah doesn't develop a fatalistic despair. He doesn't numb himself to the future. He doesn't rebel. He doesn't indulge. He leads doomed Judah into repentance.

Then the king sent and gathered together all the elders of Judah and Jerusalem. And the king went up to the house of the LORD, with all the men of Judah and the inhabitants of Jerusalem and the priests and the Levites, all the people both great and small. And he read in their hearing all the words of the Book of the Covenant that had been found in the house of the LORD. And the king stood in his place and made a covenant before the LORD, to walk after the LORD and to keep his commandments and his testimonies and his statutes, with all his heart and all his soul, to perform the words of the covenant that were written in this book. Then he made all who were present in Jerusalem and in Benjamin join in it. And the inhabitants of Jerusalem did according to the covenant of God, the God of their fathers. (2 Chronicles 34.29–32)

And he did this not for a change in outcome, not for desired result, but because God was Josiah's all-consuming joy and sovereign Lord.

This challenges me. How much of my pursuit of God has strings? Would I parent my kids in obedience to the Scripture if I knew they wouldn't grow up to follow Christ? Would I sacrifice for my wife today as a type of Christ if I knew she would leave me in the future? Would I be generous if I knew that I would never be rewarded and, in fact, people would take advantage of me? Would I encourage others to love and follow Christ even if I knew it was a pathway to hardship and suffering (which, by the way, it is)? Would I continue to preach if it was absolutely certain that it would be fruitless? Do I know him well enough, do I see him clearly enough, do I cherish him as more than enough to worship in the face of a certain dismal future?

Where your answer is, there your heart is also.

Additional Resources
Coming to Jesus without hating what we have left
No one thanks a vending maching