A Song about the devil.
Do you remember the part in "The Lion, The Witch and The Wardrobe" where the White Witch and all her ghouls are gathered around the stone table, laughing and mocking Aslan as he laid there, bound?
Well now imagine the reverse of that. Imagine gathering around with God and all the saints to watch the last few seconds of satan's life, and to celebrate his demise.
That's what this song is about.