Despite who is father and grandfather were, Yoshiyahu is unsurpassed as a champion of God worship, cleansing the kingdom of its idolatry and returning the nation to God. A process that begins in his youth, it further intensifies with the shocking discovery of the Sefer Torah. The precise identification of this Sefer Torah and its ramifications are debated amongst commentaries. However, the aftermath of this discovery is a purging of idolatry on an unprecedented scope including in the territories of the non-existent Northern kingdom that culminated in a mass celebration of Pessah in Jerusalem.  

Courtesy of the Virtual Beit Midrash, Yeshivat Har Etzion