In 1589, when María Sobrino Morillas professed as María de San Alberto, along with her younger sister (thereafter known as Cecilia del Nacimiento), in the Discalced Carmelite Convento de la Concepción in Valladolid, she and her sibling followed the path of religious life already well traveled by most of their older brothers. From the monastery, both sisters also continued another familial practice: writing. Sometimes they collaborated. On her own, the older wrote poetry in many different forms and meters, even in other languages, some of which she used to enter the secular world, by submitting verses to the certámenes (poetry contests) which were so enormously popular at that time. She also wrote plays, which she called fiestas, for the education and entertainment of her Sisters in religion, and prose, both mystical (e.g., Favores recibidos de Nuestro Señor) and practical (e.g., convent documents and biographies of family members and a religious Sister). Developed in a style uniquely her own, throughout her written work one notes the melding of popular and erudite cultures, as well as of the sacred and the profane. As the selections in the anthology Tras el espejo la musa escribe (2009), to which this essay is a companion, demonstrate, her poetry, especially the mystical verses and those that celebrate Saint Teresa of Avila, the founding Mother of her Order, most consistently displays María de San Alberto's literary skills and talent.

Intellectually and literarily the product of a decidedly humanist education, primarily taught by her learned mother, Cecilia Morillas, María de San Alberto mixed Renaissance forms and tropes with those from popular Spanish lyrical traditions in her poetry. She availed herself of a range of poetic forms—lira, romance, octava, and terceto—to express mystical and historically sanctified thoughts and feelings. A Discalced Carmelite, she clearly also felt the influence of the written works of the two most famous poets of her Order. Her verses relied on the conceptual framework and lyric tropes of St. Teresa of Avila and San Juan de la Cruz, while at the same time remaining deeply embedded in the poetically and ideologically contestatory locations of her time and place.