The Interior Castle, or The Mansions, was written by St. Teresa of Ávila, the Spanish Discalced Carmelite nun and famed mystic, in 1577 as a guide for spiritual development through service and prayer. Inspired by her vision of the soul as a diamond in the shape of a castle containing seven mansions, she interpreted life as the journey of faith through seven stages, ending with union with God.

Saint Teresa of Ávila (1515–1582), was a prominent Spanish mystic, Roman Catholic saint, Carmelite nun and author during the Counter Reformation, and theologian of contemplative life through mental prayer. She was a reformer in the Carmelite Order of her time and the movement she initiated, later joined by Saint John of the Cross, eventually led to the establishment of the Discalced Carmelites, though neither she nor John were alive when the two orders separated.