'An oven,' as in Malachi 4:1, signifies hell, where the people live who confirm themselves in false doctrines and evils of life from earthly and bodily loves.

In Exodus 7:3, this signifies exterior goods, which are natural, and are commonly called 'pleasant.'

(Odkazy: Apocalypse Explained 540)

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.