Why Óðinn is one-eyed:
His quest for wisdom is never-ending, and he is willing to pay any price, it seems, for the understanding of life’s mysteries that he craves more than anything else.
On one occasion, he hanged himself, wounded himself with his spear, and fasted from food and drink for nine days and nights in order to discover the runes.
On another occasion, he ventured to Mimir’s Well – which is none other than the Well of Urd, by the roots of the world-tree Yggdrasil.
There dwelt Mimir, a being whose knowledge of all things is practically unparalleled among the inhabitants of the cosmos.
He achieved this status by taking his water from the well, and waters impart this cosmic knowledge.
When Óðinn arrived, he asked Mimir for a drink from the water.
The well’s guardian, knowing the value of it, refused unless the seeker offered an eye in return.
Óðinn – whether straightaway or after anguished deliberation, we can only wonder – gouged out one of his eyes and dropped it into the well.
Having made the necessary sacrifice, Mimir dipped his horn into the well and offered the now-one-eyed god a drink.
The most general and obvious message of this tale is that, for those who share Óðinn's values, no sacrifice is too great for wisdom.
The fragmentary sources for our current knowledge of the pre-Christian religion of the Norse and other Germanic peoples are, however, silent on exactly what kind of wisdom Óðinn obtained in exchange for his eye.
But i can make a guess.
The fact that Óðinn specifically sacrificed an eye is significant.
In all ages, the eye has been “seen” as a poetic symbol for perception in general – consider the astonishing number of expressions, both in everyday usage and in the works of the great canonical poets, that use vision as a metaphor for perceiving and understanding something.
Given that Óðinn's eye was sacrificed in order to obtain an enhanced perception, it seems highly likely that his pledge of an eye symbolizes trading one mode of perception for another.
Painting by Scott Olesen