This excellent poem is built around two implied metaphors, in which ice is compared to hate, and fire to desire. The poem explores two different contradictory beliefs concerning how the world will end. The poem, perhaps ironically, argues that either fire (representing desire) or ice (representing hate) will "suffice" to kill us all off. This poem therefore explores the danger and threat of such emotions as desire and hate, and the way in which such emotions, uncurbed, could destroy us.
The link between fire and desire is clear, with the rhyme helping to establish the connection, but Frost compares ice to hate, which perhaps needs to be unpacked. Hate, like ice, is hard but can be melted under the right conditions. Hate might lead to violence, which could usher in the end of the world, just as desire or greed could cause isolation or division, leading to the same conclusion.
Thus this overtly very simple poem is built around two implied metaphors, which compare fire to desire and ice to hate.
This question has been previously answered here on eNotes. Here is a link for you: http://www.enotes.com/poetry-robert-frost/q-and-a/what-some-literary-devices-from-poem-fire-ice-by-87457