It's a debate between two people, who were in a relationship, ended it for whatever reason, and the song is being done from the point of view of the person who is being asked to get back with the other person. The author is saying "I don't care if you're the last person on Earth, I'll never get back with you, and how dare you talk about forgiveness after what you did to me (the person being addressed must have done something bad)!"
It's a debate between two people, who were in a relationship, ended it for whatever reason, and the song is being done from the point of view of the person who is being asked to get back with the other person. The author is saying "I don't care if you're the last person on Earth, I'll never get back with you, and how dare you talk about forgiveness after what you did to me (the person being addressed must have done something bad)!"