Albert Barnes Commentary 2 Kings 23:24

"Moreover them that had familiar spirits, and the wizards, and the teraphim, and the idols, and all the abominations that were seen in the land of Judah and in Jerusalem, did Josiah put away, that he might confirm the words of the law which were written in the book that Hilkiah the priest found in the house of Jehovah." — 2 Kings 23:24 (ASV)

Perform—Rather, establish. Josiah saw that it was necessary not only to put down open idolatry but also to root out similar secret practices that were sometimes combined with the worship of Yahweh, although the Law forbade them (marginal references). For many, these practices probably formed almost the whole of their religion.