Though out the book it shows fire as a symbol of the Germans inhumanity towards the Jews.  In the bible fire is associated with god, god seems to appear to moses as a burnign bush. The lady that had the visions of fire and no one believed her, but they all soon realized she was right after seeing the fire coming from the crematoria and seeing Nazis burning babies in a ditch. Fire was the symbol for punishment for the Jews.
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