Oeming's run was designed to be much closer to the original Norse mythology, so if some of the concepts seem cryptic and archaic, it was meant to be. But simply put, "wisdom" is seen as the greatest of power in Norse mythology. In this sense, it goes beyond simply "knowing a lot of stuff", it's basically omniscence - cosmic awareness of all things at a universal level. Even though Thor had the Odinpower for years, he lacked that wisdom to know how to use it wisely. As such, the Odinpower (which took the form of a child-like identity) turned on him, and abandoned him entirely, which is why he was just "regular" Thor at the start of Oeming's run, despite it following Jurgen's King Thor run. He had to go through similar trials to that through which his father had to go to prove himself worthy of the power and to gain the wisdom to use it correctly. A lot of the trials were reality as metaphor (poking his eyes out to see through "greater sight", hanging himself to "die and be reborn", etc.). As a bonus for doing so well, he also developed mastery of Rune Magic, which he used to own everybody in Ragnorak.
A strong case can be made, however, that the Odinpower "entity" that turned on Thor was nothing more than Thor's own guilty subconscious come to live and turned against him, and the power was his all along, he just blocked his access to it after seeing what happened in The Reigning storyline.