en_tn/2ch/34/05.md

He burned

Josiah probably commanded his workers to do much or all of this work. Alternate translation: "He commanded them to burn" or "He and his workers burned" (See: rc://en/ta/man/jit/figs-metonymy and rc://en/ta/man/jit/figs-synecdoche)

He burned the bones of their priests on their altars

This means that the bones of the priests who offered sacrifices on the altars to the false gods were burned on the altars that the priests had previously made sacrifices on.

he cleansed Judah and Jerusalem

This speaks of Josiah causing Judah and Jerusalem to be acceptable to Yahweh as if he made them physically clean. Alternate translation: "he caused Judah and Jerusalem to be acceptable again to Yahweh" (See: rc://en/ta/man/jit/figs-metaphor)