Although Machen subsequently developed greater sophistication in presenting his ideas, The Great God Pan contains in embryo almost all of his techniques and themes. The concept that a greater reality lies hidden beyond everyday events is a commonplace among fantasy writers, as it is among theologians. In subsequent works, Machen sometimes treated this ultimate reality as horrible, sometimes as beautiful. He scatters direct and indirect references to the Greek god Pan throughout his story. This mythological entity is a symbol not only of the pagan world but of a vast, soulless reality lurking behind the veil of the physical world.
The Great God Pan became notorious upon publication, largely because of its religious and sexual implications. It can be interpreted as a blasphemous parody of the story of Christ, who was the product of a union between a supernatural being and a mortal woman named Mary. There are also suggestions that the nature of Helen Vaughans evil influence is somehow sexual. Later generations have found these suggestions less shocking than Machens contemporaries presumably did.
Critics also attacked two of Machens techniques: his refusal to describe the horrors he suggests and his reliance on coincidence. The first practice is judicious, because Machen was dealing with matters that by their very nature lie beyond the scope of human language. He may also have realized that readers are capable of imagining more frightening things than even the most skillful writer is capable of describing, a fact overlooked by many later horror writers, usually to their detriment. Machens reliance on coincidence is less defensible and masks an inability to develop plot and character.
Whatever its flaws, The Great God Pan has influenced many later supernatural writers, including H. P. Lovecraft (in “The Dunwich Horror,” 1929), Ira Levin (Rosemary’s Baby, 1967), and Peter Straub (Ghost Story, 1979). It remains Machen’s best-known work.