There is a Celtic legend called the Cauldron of Changes that you can read on the website, Chalice Centre. I would like to discuss one aspect of this story that pertains to the knowledge of Soul and its transformative effects on human beings.
In the story, a peasant boy named Gwion is hired by Ceridwen to stir and keep watch over the cauldron, which she has prepared for her ugly and hapless son, Avagddu. Because of her great love for the boy, she desired to find a way to transform her son. After studying books of Druidic alchemists, Ceridwen has learned how to make a special brew that can illuminate one with the knowledge of all things, past, present, and future. She carefully gathered all the necessary ingredients into a large iron cauldron, which must simmer for a year and a day. She conscripts Gwion to keep watch over the steaming vessel.