Hi!
As I read the poem in Eclipse, I remembered I once read about it in a book, "Two Approches to Literature" or something like that. I'm not great with poetry and I'm not lucky enough to study these kind of works at school (our teacher always goes for the boring ones...), but after reading a few explainations, I start molding them to fit my own point of view.
The poem can't be a perfect fit, but this was one of those cases I tied the meaning to something I wanted, so I think it was pure genious to use it in Eclipse
I've assumed that the poetry would be recited by Bella, to express her feelings of the future.
First thing you notice is that the tone of the poem is detached - Bella is acknowledging both turns her path might lead to. (first two lyrics)
Then, she recalls her experience, lets her feelings flow through her mind and takes the side of those who favor "fire" - the allegory for her intense feelings that put her in danger so many times. But the first line speaks only about the end of the world.
As she becomes aware of the other path, she feels that the opposite of fire, ice - apathy, indifference, the feelings she starts to believe Edward had for her, would destroy her. I don't have the quote right now, but Bella says the same thing Catherine does in Wuthering Heights (can't remember if she actually quotes her) about continuing to resist, even if all else perished but not being able to exist if Edward would not stay alive. I thought the poem could relate to that. There is also the anxious feeling, very nearly turning to despair, as the assurance of the rhythm breaks up in the final 3 lines, as the paths are laid out in front of Bella. They are to be avoided, but it is beyond her control to leave them behind.
In Eclipse she still suffers of the fear that Edward would leave, so both stanzas make sense.
I'm not sure if I managed to explain what I think right... Maybe I'll edit the post if I come up with a better way to say things (coherency is not my strong point in the middle of the night - that's the time here, if you're wondering

)
Thanks for reading!