This 16th-century Spanish mystic is considered one of the most profound spiritual teachers in the history of Christianity. Father Kieran Kavanaugh. the editor of the volume. says in his introduction, "The Interior Castle has come to be regarded as Teresa's best synthesis. . . If asked to single out one work as her masterpiece, most of those acquainted with the Teresian writings would probably choose The Interior Castle," Tresa received the image of the whole book in a vision on Trinity Sunday, 1577. An early biographer says that she beheld "a most beautiful crystal globe like a castle in which she saw seven dwelling places, and in the seventh, which was in the center, the King of Glory dwelt in the greatest splendor."