The idea of a spirit who was haunted in life (as Master Gracy is suggested to have committed suicide) opening up his home to all these other wayward spirits who cannot pass on for some reason and giving them a place to rest and enjoy themselves. He could just as easily have kept to himself.
The film versions' ending, where thanks to the Evers family, all the spirits save Ramsley are freed.
"Angels in Heaven, together at last. The tale is well ended for those who have passed. Love endures all, no reason, no rhyme. It lasts forever and forever all the time."
Ezra and Emma waving goodbye.
The fact that they left with Madame Leota and the Singing Heads.