As the title implies, The Origin of the Brunists treats "the origin" of a religious-apocalyptic cult named after coal mine survivor Giovanni Bruno. Coover emphasizes the evolution, from a mining disaster in which ninety-seven miners died, of a religious faction finding its inspiration and figurehead in the taciturn survivor and his family. Thus primary social concerns addressed in The Origin of the Brunists include how hysterical and apocalyptic movements originate, and what momentum, whether social, philosophical, or psychological, propels these movements to capture a public's imagination.

Although it is a highly successful religious organization, eventually branching out into diverse districts with bishoprics and hierarchies, the Brunist movement does not originate in Giovanni's charisma or visionary skills. The leader's only qualification is that he survived in a mine chamber in which six other men suffocated. Actually, Coover's description of the explosion in Deepwater Number Nine suggests that Bruno was usually isolated because of his habitually not fitting in with the miners and his cowardice when the disaster struck. Once rescued, Giovanni seems a semi-catatonic invalid who occasionally utters cryptic phrases like "Mount of Redemption!" and mentions having seen the Virgin Mary while trapped in the mine (seeing holy figures is a phenomenon frequently reported by rescued victims of cave-ins, especially those whose oxygen supply is dangerously low and who fear imminent death). Bruno's main qualification for cult leadership is his nodding assent to leading questions by townswomen hungry for new and vital religious experiences. To Eleanor Norton's question about whether he is "the One who is to come," Giovanni nods; to his sister's assumption that he has been transformed, perhaps possessed by a divine spirit while trapped in the mine, he gives tacit consent. Therefore, one of Coover's main themes in The Origin of the Brunists is the degree to which charismatic movements result not from the force of the leader but from the hunger of potential cult members for revelation.

A corollary of this theme is the degree to which the cult members' need for revelation and their consequent imposition of "redeemer-status" on Bruno result from their limited and frustrated lifestyles. Coover's persuasive descriptions of the tedium and viciousness of the daily existence of the miners' and merchants' families in the small midwestern town where the disaster occurs lend credibility to the willingness among potential Brunists to believe in anything that promises to make their lives special. When the characters' happiness depends on chatting with one another in a lunchroom, watching high school basketball games, making out in parking lots, and submitting to the mine for economic survival, it is little wonder that any movement that offers wonder and special-ness, especially with hints of an end to creation and exclusive salvation for those who make up the Brunists, will gain a following.

Moreover, the Brunists' widespread popularity is a creation of the media. A spectacular event in an insignificant place like West Condon motivates the media to transform a collection of religious compensators into a cult with international importance. Every public event involving the Brunists, including their awaiting the end of the world, is covered by television and national newspapers. A local journalist and philanderer, Tiger Miller, poses as a convert to get the scoop on the doings of the Brunists and to sell exclusives to national news services. It is the self-serving competition among members of the press that transforms the activities of a cult of local misfits and zanies into an international movement.