Robust, energetic, and, as Cusins suggests, the incarnation of loveliness, Barbara is the play's savior. She begins the play as a major for the Salvation Army who is peacefully convinced of her mission to redeem mankind through Christian dogma. Her father's arrival forces her to reevaluate her beliefs. The demonstration of his power over the Army will force her to realize that the wealthy, rather than God, hold the world and its salvation in their hands. Utterly disillusioned, she sheds her uniform and abandons her work. Her Father has forsaken her, leaving Undershaft in His place.

Soon thereafter, however, Barbara's visit to Undershaft's ideal community of Perivale St. Andrews will lead her to recognize the armory as necessary to man's redemption, bloodshed necessary to salvation, evil necessary to good. For Barbara, "life is all one," and she can return to the Army with her new father's gospel in mind. As in most conversion narratives, Barbara's epiphany demands a death—thus "Major Barbara will die with the colors"—and her rebirth. She ends the play by regressing to girlhood, calling for her mother, tugging at her skirts, and asking her to help choose her new house in the planned community.

As Undershaft insists, Barbara's own "inspiration," rather than the truth of Christianity, makes her man's savior. The daughter of a foundling, Barbara ostensibly lacks social class and comes "straight from the heart of the whole people." She considers herself universal, a woman who can serve as savior to everyone. Perhaps this universality explains why Shaw does not particularly describe her in the stage notes. Ironically, Barbara's proclamation would blatantly deny the class status that makes her Salvationist career possible. As revealed by her assault on Bill Walker in Act II, Barbara is not only compelling because of the "inspiration" she exudes, but also the authority she wields in her aristocratic heritage, polished speech, and professional manner.