"Day" is about what it means to be human; all of the beautiful things, the awkward and ugly things, and the inherent unity we all share.  Furthermore, it is about the end of humanity, when the world turns on its own head and pushes our species to the peak of desperation.  The climax scene describes the entire population of the world on a huge rock, with enormous waves washing people away and storms causing global chaos.  With each new wave, everyone cries out with wordless desperation.  But, ultimately, "Day" is about maintaining perseverance, optimism, and love no matter what happens.  Also, there is a hidden message in the song somewhere... o.o      

~TheO~