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.

826. There were certain members of both sexes from the so-called Christian world who during their lifetime had imagined adultery to be not only permissible but also sacred. In so doing they upheld collective marriages, as they irreverently termed them, under a pretence of holiness. I saw that they were sent to Gehenna, but when they got there a change took place. The fiery glow of Gehenna, which is decidedly red, turned decidedly white on their arrival, and I perceived that they did not fit in there. Consequently that unmentionable bunch was removed from that place and taken down to a quarter at the back. I was told that they had gone into another world where they would be immersed in stagnant waters, and from there on into a new Gehenna that had been provided for them. I heard in this Gehenna something like a hissing which was indescribable. But the hissing or hum of Gehenna was duller than that of those people who had defiled holiness by acts of adultery.