Mankind has been consumed by desire(fire) and hardened by hate(ice). The poet says the world will end in war or in fragments caused by the ridgidity of heart and head. What in your opinion can establish permanent peace on earth.
The poet mentions that both fire and ice are probable ends of this world. While he talks about how fire represents desire and can therefore be a cause of the end of the world, he also mentions ice in between to symbolise that the coldness and indifference towards one another will also be enough to end the world. In the second stanza, he says that he knows of enough hate in the world to be sure that even destruction through ice would be sufficient to bring about the end of the world.
Only love, equality, mutual understanding and sympathy for one and all can help in establishing peace on the earth.