There's no need to explain this, is there? We all lose people we love and there's no adequate way to explain the feeling so, inadequately, another song of loss written in the spring of 2011. So, the theory goes, loss leads to a fired imagination which then lights the neural pathways that lead to songs.
Along with Invisible Thread, this is the most important song on the album to me but that's only because it's the most directly personal, not because it's intrinsically better. It's all a matter of taste.