Because the Romans never crossed the way to Ireland, nor to the present Scandinavia, the religious experience of these peoples survived longer than in the rest of the European continent. Consequently, it was also more difficult to implement Christianization once it had taken place in Rome. Irish civilization was only found in the 5th century AD by the Bishop Palladius. This in turn sent the bishop Patrick to the island, who took on the conversion of the Irish.
The Celts also saw this people as 'a different kind of people', not so much 'higher' or 'better' than themselves, but more as figures who could do things that they themselves could not. Similarly, this people were not immortal, but were in contact, for example, with the souls of the dead and the spirits of nature. They knew the gates to the Other World and other mythical places. These worlds were parallel to the earthly world, but invisible to humans. In addition, they still possessed their great knowledge and magical powers that made them an interesting ally.
Different types of
Although Aos Sí generally refers to the people from the Other World, there are still differences. One of the most famous among them is the Ban Sí, or banshee, which literally means 'lady from the Sidhe'. When she is present in this world, death is often near. Her deafening whining and crying announces that someone will soon die. Her Scottish counterparts are the Bean Nighe, the laundromat who washes the blood from the clothes of the person whose fate faces death.
The Sluagh Sidhe are lost or damned elves who continue to wander around. We also have such a phenomenon in our regions, but we call them white wives. These female ghosts are coming back all over Western Europe. Sometimes they predict the transition of life, birth or death. In other countries such as France, they are rather wise women who see more that which the naked eye can release. They are seen as female beings who often lure men or spin around their fingers.
That's what happens to a Leanan Sidhe, who seeks the love of people. However, it is a forced love. When the opposing party (usually male) refuses, she will submit to obtain love. If the opposing party does go along with her feelings, he will always be hers. But as the Elf continues her life, the other party will languish. She is the overwhelming muse, who floods her worshippers with inspiration until those who cannot lose out of frustration and go to death. These persons are therefore expected to live a full and inspiring, but short life. Often they are also a source of inspiration for those who live after them.
When Christianity took place after the arrival of the bishop Patrick, people also continued to hold on to their old beliefs. For example, they believed when one had a difficult baby, who turned out to be dissatisfied or difficult to handle, this was the result of a switch with an elves child. Often people tried to reverse the switch by different methods. In reality, of course, the switch never took place. In other words, the child found peace and life went on, in other words it was carried to a fairy place or hill in the hope that the Sidhe would find it and return the original child. The latter, of course, could not happen, but the parents then made peace with the idea that their child had the privilege of living with the elves
The drama around changeling children is beautifully displayed in Episode 10 of Outlander. In this excerpt, Jamie explains the extent of the faith in it to Claire, after trying to save a changeling.
Cesair: Ireland's first finder
Although Irish folklore often looks like a fairy tale, there is also often a connection with Christianity. For example, there is Cesair, who would have been a granddaughter of Noah. But when Noah received the message from God to build his ark, Cesair and her father were denied access to it. Then Cesair decided to build an ark himself and gathered in it many women, each with their own talent. She set course for the Inis Fail, or the land of destiny, Ireland. Since this island had not been inhabited until then, no sin could have taken place and therefore it would be safe from the flood. But unfortunately, after some time of reign Cesair died of a broken heart and when the flood came flooded the island along with the rest of the world. Only Banba and Fintan would survive the disaster and eventually give life to another mythological people the Formorians.