When we say the Gods fight with Giants, how do we mean that? The multipurpose preposition “with” could mean “against”, “alongside”, or “using”. Robert Blumetti sees this action as the interplay of force with form that is responsible for all creation, so it would be a shallow understanding to take this interplay as mere opposition. Force must be used creatively, so while at times legends may present Gods as fighting against Giants to subdue them, Giants are often represented as having particular powers that may be used by the Gods, so that the Gods may wind up fighting alongside Giants or using them. So it is with Mimir, a frost Giant whose name is cognate with words in Indo-European languages for mind, memory, and related concepts. Mimir had exclusive possession of a well that drew from a flow feeding the Yggdrasill from out of Jotunheim. Drinking from that well kept Mimir “au courant” as the French say, and Mimir's mind distilled the material from that current into wisdom.
The legends portray Odin as seeker of all knowledge, and willing to make great sacrifices for it. So it was inevitable that he make a visit to the well and ask to drink from it. Mimir allows this at the price of one of Odin's eyes. The Eddas have it that Odin cast that eye into the well itself before drinking from it. My father told me his father used to say of a particular one-eyed individual, “He could see more with that one eye than others could with four,” referring to eyeglass wearers as four-eyed. So it is with the All-Father, as one can interpret the eye in the well as the one that sees so much.
The legends also tell of a war between the Aesir and Vanir races of Gods, in which Mimir is on the side of the Aesir. Mimir was beheaded as a consequence. Some accounts would leave one to think his beheading is as a combatant. The more florid account has it that the war ends uneasily, with lingering suspicions requiring an exchange of hostages who had been in leadership positions. The Vanir receive Mimir and the God Hoenir, and proceed to employ Hoenir at what he appeared to be good at, which was giving advice. However, Hoenir is wishy-washy about advice when he can't consult Mimir first. This disappoints the Vanir, but instead of taking it out on the apparent poseur Hoenir, they behead Mimir in spite. One might think they would have delivered his head to the Aesir as a message, but the legends don't specify that.
No matter how he got Mimir's head, Odin uses magick to preserve it and allow it to speak. That is, Odin keeps Mimir as a counselor even without a body. Blumetti cautions us not to take the image at the right, where Mimir's head is perched on the well, literally...but none of the legends should be taken literally anyway. If the artist chose to put representations of Odin, his eye, the well, Yggdrasill, and Mimir's head together for purely symbolic or artistic reasons, the resulting meanings are rich enough. However, I think it unseemly to have Mimir's head tucked under Odin's arm or in his baggage all the time, so I think Odin would park Mimir's head in its rightful place as shown, and that he (and Heimdall) would continue to visit him and share drinks from the well. All that's missing is the Gjallarhorn for them to dip.
The symbolism of Mimir's well as an endless fount of knowledge, and hence a label for sagacious writings, is maintained in many places today, as an online search will reveal. Balder Rising is no exception, as we present...
The Well of Mimir School
...being a collection of essays (in PDF) by Robert Blumetti that he adds to from time to time: