'Ah, Lucifer, This Is the Place'

Our ancestors used to distinguish for themselves between the devils and the fairies. The only ones that can get into heaven are human beings, if they behave themselves. Fairies have no red blood because they weren't human. And it explains what you asked about changelings. They want to get back into heaven because they know what heaven is like,. but they can't. It's an awful pity people haven't a sense of humour about their own religion.