You can probably read this poem on many levels. One of them might be as a comment on relationships gone bad, or which could go bad. The "fire" option may represent the passions --- greed, anger, lust, yelling, confrontation --- you get the idea. Any of these can destroy a relationship (or a world). On the other hand, the "ice" --- chill in relationship, ignoring the other, not communicating, perhaps even hatred --- these would do just as well in destroying a relationship (or a world).
What is not said, but suggested, is that there must be a middle that can prevent either of these from happening, either the first time or the next. It's interesting to see how this poems works not so much by what it says, but by what it doesn't say.