Some say the world will end in fire,
Some say in ice.
From what I've tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
Frost may be alluding to Dante’s  Inferno  (in which both fire and ice are punishments in Hell) or to scientific accounts of Earth’s fate billions of years from now. The planet will either be consumed by the Sun, or survive as a cold and lifeless rock. 
 
 Alternatively, the later references to desire and hate suggest that Frost may intend a nonliteral meaning here. Maybe he is using the connotations of fire and ice to comment purely on human relationships rather than the apocalypse. 
 “In an anecdote he recounted in 1960 in a "Science and the Arts” presentation, prominent astronomer Harlow Shapley claims to have inspired “Fire and Ice”. Shapley describes an encounter he had with Robert Frost a year before the poem was published in which Frost, noting that Shapley was the astronomer of his day, asks him how the world will end. Shapley responded that either the sun will explode and incinerate the Earth, or the Earth will somehow escape this fate only to end up slowly freezing in deep space. Shapley was surprised at seeing “Fire and Ice” in print a year later, and referred to it as an example of how science can influence the creation of art, or clarify its meaning." 
 In Norse mythology, ragnarok, or the end or the world, in which the Gods (so humans, basically) must fight and then shuffle off to different patches of the rubble, both ice and fire feature in the show of destruction, while in christianity, it is mostly just fire. Frost could be referencing religious contradictions and arguments between religions, on the nature of humanity’s curtain call in the humorous tone of this poem, suggesting that such debates, while interesting, are more like eyes that  don’t line up  rather than totally divergent views.
Fire and Ice