The psychological rule says that when an inner situation is not made conscious, it happens outside, as fate.
That is to say, when the individual remains undivided and does not become conscious of his inner opposite, the world must perforce act out the conflict and be torn into opposing halves.
(From Christ, A Symbol of the Self; CW 9ii, par. 126.)
The Norns are three women who shape the life of each man from his first day until his last, and they determine the moment of his death.
The Norns live in Ásgarð by the Well of Urð, where the gods meet each day in council. Of the three women, Urð is old and decrepit, looking backwards to past events and people. Verðandi is young and active, looking straight before her. Skuld is closely veiled, and looks in a direction opposite to where Urð gazes.
The Norns carve men’s fate on a stave of wood, in much the same way Norsemen might carve their individual marks on pieces of wood before throwing them together to draw lots.
In Gylfaginning, Snorri Sturluson writes that other norns, descended from the Æsir, dwarves, and elves, visit each new-born child to determine its life. Good norns grant a good life, while malevolent norns grant lives filled with misfortune. (Source)
Urth is the guardian of a sacred well at the base of the World Tree. Each day as the roots of the World Tree are worn away by care and ill-will, the Norns take up some earth, moisten it with water from Urth’s Well, and place this clay with care on the roots of the tree, healing and renewing it.
The tree that links all worlds draws up water from the well, up through trunk and branches and leaves, and the well’s water falls again from the tree as the dew, where it re-enters the well again to renew the cycle.
I have been used to considering Norse mythology as pretty much the most brutal and patriarchal of all mythologies. And yet, here at the center of its cosmological myth, with the sacred Well and the holy Tree, are images of the three Goddesses doing their work of healing and renewal. It is one of the loveliest images in all mythology. (Source)
Why are there are three roots, three well, three norns?)
(from Marie Louise Von Franz, Number and Time, p.33):
Numbers as archetypal structural constants of the collective unconscious possess a dynamic, active aspect which is especially important to keep in mind. It is not what we can do with numbers but what they do to our consciousness that is essential’
(from Psychology and Religion: East and West CW 11, par. 179):
One is the first from which all other numbers arise, and in which the opposite qualities of numbers, the odd and the even, must therefore be united; two is the first even number; three the first that is uneven and perfect, because in it we first find beginning, middle and end.
(Summary of Yggdrasil and the Three Wells:)
Yggdrasil is mentioned in two books in the Prose Edda; Gylfaginning and Skáldskaparmál. In the Prose Edda book Gylfaginning, the Yggdrasil is introduced in chapter 15. In chapter 15, Gangleri (described as king Gylfi in disguise) asks where is there the chief center or holiest place of the gods. High replies “It is the ash Yggdrasil. There the gods must hold their courts each day.”
Gangleri asks what there is to tell about Yggdrasil. Just-As-High says that Yggdrasil is the biggest and best of all trees, that its branches extend out over all of the world and reach out over the sky. Three of the roots of the tree support it, and these three roots also extend extremely far: one “is among the Æsir, the second among the frost jötnar, and the third over Niflheim. The root over Niflheim is gnawed by the wyrm Níðhöggr, and beneath this root is the spring Hvergelmir.
Beneath the root that reaches the frost jötnar is the well Mímisbrunnr, “which has wisdom and intelligence contained in it, and the master of the well is called Mimir.” Just-As-High provides detail regarding Mímisbrunnr, and then describes that the third root of the well “extends to heaven,” and beneath the root is the “very holy” well Urðarbrunnr. At Urðarbrunnr the gods hold their court, and every day the Æsir ride to Urðarbrunnr up over the bridge Bifröst. (Source)