He was Harvey Dent that had Two Face waiting inside him. Two Face was just waiting until Harvey broke, once he did. Two Face emerged, and Harvey Dent was gone. The message is clear, humanity can be the best versions of themselves, fighting amongst the daily hardships of life in perseverance to be as good as only they will allow themselves to be. But deep down, we all have a two face awaiting our breaking point.
Meh, I guess only to the weak minded that are easily deceived, like those from Arkham Asylum.