Fire, in the spiritual sense, can mean either love or hatred depending on the context, just as natural fire can be either comforting in keeping you warm, or scary in burning down your house. Our language reflects this, too -- we use concepts like a smoldering hatred or a burning love. So fire signifies a love, either a good love of the neighbor and to the Lord, or, in a bad sense, selfish love of oneself that, if unchecked by conscience, leads to hatred of anyone that opposes it.

568. Spiritual heat in man is the heat of his life, because, as was said above, it is in its essence love. This heat is what is meant in the Word by "fire," love to the Lord and love towards the neighbor by "heavenly fire," and love of self and love of the world by "infernal fire."