Dear student,
The theme of the poem is whether the world will end in fire or it will freeze. The poet says that some people think the world will come to a fiery end while others think it will freeze. He could be talking about the literal end of the world, but he is also talking about the power that human beings have to harm or destroy one another. It could also mean the power of love which brings peace and harmony and the emotion of hate which brings ruin.
Regards