What is the importance of "the soul" in the novel, The Woman Who Lost Her Soul?

The question of whether the human soul exists is part of one of the narrative’s key themes. It also actively manifests in the lives of several of the main characters (including Dottie, Harrington, and Eville Burnette), while experiences of the soul, primarily negative, can be seen indirectly in the lives and experiences of others, including Dolan, Parmentier, and perhaps most significantly, Steven Chambers.