It all started with the reading of God's Word. I'm talking about the revival which came in the days of Josiah. The revival was brought on by exposure to the truth... the written truth; the written revelations of God. Hilkiah, Shaphan, Josiah and eventually the whole city of Jerusalem had either read the prophecies or had heard them read by someone else. The effect was drastic and wonderful. Josiah (and the people with him) put down the worship of Baal, drove away the perverts, ended human sacrifices, fulfilled the prophecies against the ancient altar of Jereboam (I Kings 13:2), desecrated the evil shrines which Solomon had erected centuries earlier, executed the leaders of false religion and reinstituted the feast of the Passover. That last accomplishment was perhaps Josiah's greatest one. Obviously, the nation had altogether ceased from celebrating Passover. Josiah brought it back.
Now, Josiah didn't just renew the feast, he did it right. I mean, he did it BIG! 2nd Kings 23:22 says that there had never been such a Passover feast as there was that first time that Josiah celebrated the Exodus from Egypt. It seems that he took to heart the words of his ancestor, Solomon. Ecclesiastes 9:10 basically says that if we are going to do something, we should do it with gusto; anything worth doing is worth doing well. So, Josiah commemorated God's powerful deliverance of the Jews from Pharoah in a way that made a statement and had a lasting impact.
A good friend just asked me what the significance of 2nd Kings 18:4 & 5 is. These verses exalt King Hezekiah to a position of superlative importance in Jewish history. In the matter of faith, there was no monarch equal to Hezekiah... not even David. However, in this matter of repentance and revival, no king superseded Josiah (II Kings 23:25). The faith of Hezekiah temporarily reversed the rotation of the globe. The repentance of Josiah temporarily reversed the spiritual direction of a nation. Which one is the greatest accomplishment? Which one is the most difficult and significant?