Throughout the colonial period of Mexican history, cloistered nuns wrote spiritual journals at the request of their confessors. These documents were read and scrutinized, not only by the confessors, but also by others in the hierarchy of their Orders. They are important sources of study for historians in that they provide a window into the religious culture of the times and the spiritual mentality of their authors. This thesis will examine one such record, discovered in a collection of volumes at the Historical Franciscan Archive of Michoacán in Celaya, Mexico. The diary covers eleven months of 1751 in the life of a Franciscan nun -- believed to be María de Jesús Felipa who kept such records over a period of more than twenty years. María de Jesús Felipa was a visionary who experienced occasional ecstatic states. Through her contacts with the spiritual world, she pursued her own salvation and that of those most specifically in her charge: members of her own community -- the convent of San Juan de la Penitencia in Mexico City -- and the souls in purgatory. These encounters propelled her into different frames of time and space -- moving her into the past and the future, and transporting her to bucolic and horrific locations. Her diary ascribes meaning to these encounters by tying them to her life and her relationships within the convent. Her diary of 1751 also indicates that this spiritual activity and the records she kept brought her to the attention of the Inquisition. The thesis argues that, because of its cohesiveness of thought and consistency of focus, the diary effectively casts its record keeper as author of her own life story. A close reading reveals the inner thoughts and perceptions of a distinct personality. Her first-person account also reflects the character of Christianity, the impact of post-Tridentine reforms and difficulties in the governance of convents in eighteenth-century New Spain. Although always arduous and often unpleasant, writing provided Sor Maria with an opportunity to establish her integrity, exercise control, and justify her thoughts and actions as she pursued her vocation. Writing under the supervision of a confessor, María de Jesús Felipa was her own person. In its organization and focus, her diary resolutely records a struggle for self-determination within the limits imposed by the monastic vows of obedience, chastity, poverty and enclosure.