The Key to Everything by May Swenson

This is a really incredible poem that's all about love and sacrifice and so many other Supernatural themes. But I can't figure out which characters or pairings it works for. At the beginning, it seems like Dean talking to Sam, but towards the end it's Castiel talking to Dean, and somewhere in the middle it's Sam and Cas. So I want your thoughts about this poem. Who is it about and which community should I post it to?

( Is there anything I can do or has everything been done )