He considered sulfur to be the active principle in the opus and thus of human life. He equated sulfur with what psychology calls the motive factor: on the one hand, the conscious will; on the other, unconscious compulsion.
Hillman summarizes Jung’s core psychological reading of sulfur as the driving force of both conscious volition and unconscious compulsion, with affinities to both Devil and Christ.
, Alchemical Psychology, 2010thesis