There is much to explore about the world of faery and a brief insight might be helpful at the beginning.
When the early Catholic monks arrived in Ireland they were preaching St. John’s teachings of the divine in all things. These teachings easily found alignment with the Irish people who, with a strong shamanic heritage, believed in sacred energy flowing through all things. And the two happily coexisted for several hundred years, until Rome decided Catholic teachings would reflect St. Peter’s teachings of finding divinity only through the church.
This created a problem of how to shift and transform the entrenched Irish belief system in the spirit realms – human, plant, Earth, and animal. They had to create a story that would allow for the demonization of the sacred. This was tricky business.
In 1887 Lady Wilde wrote about the solution in her book, Ancient Legends, Mystic Charms, & Superstitions of Ireland. “The Sidhe, or spirit race, called also the Feadh-Ree, or fairies, are supposed to have been once angels in heaven, who were cast out by Divine command as a punishment for their inordinate pride.”
Fallen angels. Brilliant, really. At once acknowledging a divine nature but creating the story of demonization. Now, with demonic nature, these otherworld spirit energies of the Earth, plants, animals, and human ancestors are no longer to be trusted or considered allies. Yes, they might occasionally provide benefit but watch out, they will turn on you. And this capricious if not malevolent nature is now firmly embedded in Irish faery folklore. For Irish spirituality this solution was both effective and tragic.