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.

566. WHAT HELL FIRE IS AND WHAT THE GNASHING OF TEETH IS

What eternal fire is, and the gnashing of teeth, which are mentioned in the Word in reference to those who are in hell, scarcely as yet has been known to anyone, because they have thought materially about the things that are in the Word, not knowing its spiritual sense. So fire has been understood by some to mean material fire, by others to mean torment in general, by others remorse of conscience, and others have held that it is mentioned merely to excite terror in the wicked. Likewise some have supposed the gnashing of teeth to mean actual gnashing, and some only a horror, such as is excited when such a grinding of teeth is heard. But anyone who is acquainted with the spiritual meaning of the Word may know what eternal fire is, and what the gnashing of teeth is; for every expression and every meaning of the expressions in the Word contains a spiritual meaning, since the Word in its bosom is spiritual; and what is spiritual can be set before man only in a natural way of expression, because man is in the natural world and thinks from the things there. Therefore it will now be told in the following passages what is meant by "eternal fire" and "the gnashing of teeth" into which the spirits of evil men enter after death, or which their spirits, then in the spiritual world, endure.