I did a deep dive into Celtic Christianity to write my chapter on "Celtic Enchantments" in Hunting Magic Eels. I'm proud of that chapter for its scholarly integrity and academic rigor which avoids a lot of the commercialized nonsense one finds among those who sell visions of "Celtic Christianity" to spiritual-but-not-religious audiences.
Leading a three week class on Celtic Christianity has caused me to return to the pre-Christian Celts and the Irish monastic tradition. I'm wanting to lecture a bit on some of the peculiarities of Irish folklore and belief concerning the supernatural realm. And so, I've been learning a lot about fairies.
One of the best places to start if you want to learn about the fair folk of Ireland is The Fairy-Faith in Celtic Countries by Walter Evans-Wentz. Published in 1911, The Fairy-Faith in Celtic Countries was Evans-Wentz's Oxford doctoral dissertation. As an anthropological study, Evans-Wentz traveled through Scotland, Wales, Cornwall, the Isle of Man, Brittany, and Ireland collecting stories, folklore, and firsthand accounts of fairies. From these testimonies, Evans-Wentz concludes that the fairy-folk are real, or at least evidence of a supernatural realm existing alongside our own. Evans-Wentz places much of the blame for the loss of the fairy-faith among the Celtic peoples upon modern urban and industrial life. Modernity has deformed us and made us unnatural. Evans-Wentz writes:
The great majority of men in cities are apt to pride themselves on their own exemption from ‘superstition’, and to smile pityingly at the poor countrymen and countrywomen who believe in fairies. But when they do so they forget that, with all their own admirable progress in material invention, with all the far-reaching data of their acquired science, with all the vast extent of their commercial and economic conquests, they themselves have ceased to be natural. Wherever under modern conditions great multitudes of men and women are herded together there is bound to be an unhealthy psychical atmosphere never found in the country...they have lost all sympathetic and responsive contact with Nature, because unconsciously they have thus permitted conventionality and unnaturalness to insulate them from it.
Most of the evidence also points so much in one direction that the only verdict which seems reasonable is that the Fairy-Faith belongs to a doctrine of souls; that is to say, that Fairyland is a state or condition, realm or place, very much like, if not the same as, that wherein civilized and uncivilized men alike place the souls of the dead, in company with other invisible beings such as gods, daemons, and all sorts of good and bad spirits. Not only do both educated and uneducated Celtic seers so conceive Fairyland, but they go much further, and say that Fairyland actually exists as an invisible world within which the visible world is immersed like an island in an unexplored ocean, and that it is peopled by more species of living beings than this world, because incomparably more vast and varied in its possibilities.