Brass and iron as in Isaiah 48:4 and Daniel 7:19 signify what is hard.

In Genesis 4:22, brass signifies natural good. (Arcana Coelestia 421)

In Numbers 21:9, this signifies the Lord's divine natural. (Apocalypse Revealed 49)

Brass also signifies the good in man's natural and the sensuous in the Lord. (Arcana Coelestia 197, Apocalypse Revealed 49, Apocalypse Explained 705)

(Odkazy: Apocalypse Explained 70)

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.