The poem is literally saying that either the world wil die because of fire (desire) or ice (indifference). Fire would consume the world because everyone want's something and most people will never budge from that direction. Indifference would also kill us because if nobody cared about another person then if something bad happened then noone would fight together and the world would be threatened. The indifference can kill us because everyone only cares about themselves. this is demonstrated in the world today because we are involving ourselves with the Iraq War and not paying attention to other people's sufferings.