Josiah was among the greatest kings that ever reigned in Jerusalem. In 1 Kings 22, we will see what motivated King Josiah, namely the accidental discovery of an unusually important book.
I’m not very familiar with the French Confession of Faith, and I suspect I’m not alone. Nonetheless, it apparently has some real gems within it. For example:
We believe that the Word contained in these books [viz., the Bible] has proceeded from God, and receives its authority from Him alone, and not from men. And inasmuch as it is the rule of all truth, containing all that is necessary for the service of God and for our salvation, it is not lawful for men, nor even for angels, to add to it, to take away from it, or to change it. Whence it follows that no authority, whether of antiquity, or custom, or numbers, or human wisdom, or judgments, or proclamations, or edicts, or decrees, or councils, or visions, or miracles, should be opposed to these Holy Scriptures, but on the contrary, all things should be examined, regulated, and reformed according to them.”
… The French Confession of Faith, article V. 
This was quoted in The Christian Quotation of the Day, which I invite you to check out for yourself.