He was raised by people who sacrificed children and were ultra-wicked, becoming king at age 8 because his own father was murdered. One can only guess what they did to him as a child. He would have been controlled, as a ruler.
The prophet Jeremiah was called to preach against what was being done under his rule.
Josiah consulted a prophetess regarding his death. She said he would die in peace. Yet he was shot on the battlefield and died during the siege of Jerusalem, where the city was taken, later burned, and all the woes pronounced upon it by Jeremiah were executed.
And yet, here we are, to this day, talking about how great his reforms were. Margaret Barker talks a lot about what they consisted of. We have her speak at LDS conferences and such. But the funny thing is, we tend to twist her conclusions to suit our own Deuteronomical assertions. It’s bizarre.
For instance, she talks about how Josiah’s people removed the tree of life (symbolized in the branched lampstand) from the holy place of the temple, as well as the anointing oil that was said to have come from and been a product of the tree of life. These are both directly linked to Lady Wisdom, the Great Lady of the temple, so-called weaver of the veil. There was an attempt to completely remove her from scripture by the Deuteronomists of Josiah’s day, and to remove all traces of her from the temple. Even when BYU scholars elaborate on Barker’s work, they strangely leave out all mention of the Woman and focus instead on the high priest. I will include a stellar example in a comment to follow.
But anyways...it must an increasing awareness of how wicked rulers/priests destroy children and groom them for their use that it occurs to me that there was very little chance King Josiah acted in a way that furthered God’s work. And the fruits of his reign would suggest the same.
(From Forerunner Commentary)
It will be helpful to set the stage for Josiah's appearance in 639 BC. The northern ten tribes, Israel, are in captivity, having been conquered by Assyria about 80 years earlier during the reign of Judah's king Hezekiah. A good king who tried to follow God, Hezekiah rules for 29 years. His son Manasseh, however, is a very evil man. During his 55 years on the throne, he leads the people away from God, even to the extent of sacrificing children. Coming as it does after the 29 years of obedient leadership under Hezekiah, Manasseh's reign provides a clear contrast to the people.
Though Manasseh exercises corrupt leadership, it appears the people willingly follow. In II Kings 21:9, God comments, "But they [the people] paid no attention [to God's laws], and Manasseh seduced them to do more evil than the nations whom the LORD had destroyed before the children of Israel." Because of this, God says in verses 12 and 15, "Behold, I am bringing such calamity upon Jerusalem and Judah, that whoever hears of it, both his ears will tingle . . . because they have done evil in My sight and have provoked Me to anger. . . ." God prophesies severe punishment for Judah because He sees it is plain that the people themselves are corrupt, not just their king.
After Manasseh's death, his son Amon rules for only two years, assassinated by his own servants. And so eight-year-old Josiah ascends to the throne of Judah. His story begins in II Kings 22:1, "Josiah was eight years old when he became king, and he reigned thirty-one years in Jerusalem." Through the chronicler, God comments, "And he did that which was right in the sight of the LORD, and walked in all the ways of his father David; he did not turn aside to the right hand or to the left."