Both or None

At one time there was hope in the world this story describes. And that hope was light. But then it disappeared into eternal darkness. It starts with "morning's song and mourning's curse, to both or none we must belong" because you can't have joy without pain unless you are dead and feel nothing. It ends after the light is gone with "morning's curse and mourning's song" because since it is gone forever the memory of the morning causes pain and is a curse. And the song is mourning because it is the most joyful thing left.