The exchange between Cusins and Undershaft begins the full elaboration of what Shaw dubs in the play's preface the "gospel of Saint Andrew" and Cusins's conversion to this dogma. As Shaw observes with dismay in the preface, many critics have tended to identify too readily these discussions as having Nietzsche's ideas in their subject matter. We should note that the apparent similarities between, for example, Nietzsche's superman and Undershaft's mad one or the Dionysian and Cusins's worship of Dionysus not self-evident and that any discussion of the two authors demands the careful examination of both bodies of work.
In the men's tête-à-tête, Undershaft poses the existence of great, mad figures who stand above the herd, such as the millionaire, poet, and savior, or himself, Cusins, and Barbara. Only these inspired madmen determine the course of the world, controlling life and death itself.
Declaring his fatherly love, Undershaft claims alliance with Cusins and insists that they must win Barbara. She is his heir, the daughter who would carry forth the Undershaft's gospel in his wake. As we will see, however, it is the father's coeval, Cusins, who will ultimately become Undershaft's true heir, becoming the foundling who assumes the company name and, unlike the earnest Barbara, is "in" on all of the calculating father's machinations. Note how Barbara figures as a jointly owned commodity of sorts that binds the two men together. Cusins casts her as a possession he must have. Later, Undershaft will twin her with his ducats.
For Undershaft, none of the trio needs to work under the sign of Salvation Army. He knows that Barbara's greatness does not come from some doctrine, whether the Army's or otherwise, but from her inspiration. The army is only her instrument.
Undershaft also knows that Cusins—self-described as a "collector of religions"—does not believe in the Army either but uses it the drum for his poetry, as a means of bringing ecstasy to the masses. Cusins is a worshipper of Dionysus, the Greek god of wine and deity of excess, annihilation, and ecstasy. Through the Army, he would bring Dionysus's poetry into the street, where it serves as a "pathfinder of salvation." As a student of Euripides, the most famous democrats of the Greek tragedians, Cusins ostensibly does this work for the love for the people. Part of the perversity of the play's conclusion will lie in Cusins's reconciliation of this love with his decision to join the Undershaft firm.
In contrast, Undershaft has no love for the people themselves. He does cling, however, to the redemption of society. As he scandalously declares, in the gospel of the millionaire, this redemption is contingent on Money and Gunpowder. All social goods are contingent on the "rich, strong, and safe" life only a millionaire can provide. Undershaft will reveal the extent of the millionaire's power in purchasing the Army in the following scene and thus robbing Barbara of Bill's soul. Indeed, as he tells Cusins, the Army already serves his interests, colluding in the domestication of the masses that keeps him in power.