The overarching theme of Pan is the primal nature of humans. The main character of the novel is a man who despises the cultured social class and social norms in general. He despises society so much that he chose to live "off the grid" in a rural area of Norway. He hunts, fishes, and develops the temperament of a "wild man of the woods."

The theme of the novel—the primitive nature that we can revert to—is personified by Glahn, the main character, and the entire novel is essentially about this personification, regardless of the other characters in the story. Glahn represents sexual promiscuity, infidelity, callousness, pride, and ego. Glahn's character is a study on the extremes of the human ego. He doesn't seem to truly love the women in his life; he only desires them to be in his possession. His competitive nature with other males shows the dynamics of "alpha males" found in nature. Glahn has become what he sought in the beginning: a man who has regressed into an animal-like nature.

In modern psychology, Glahn would likely be classified as a sociopath (with antisocial personality disorder) or perhaps diagnosed with bipolar disorder, the characteristics of which he exhibits throughout the narrative. However, in the end, his chaotic mentality and behavior led to his own death.