The Interior Castle by St. Teresa of Avila presents a remarkable description of the entire spiritual life from the first release from mortal sin into Sanctifying Grace through the Mystical Marriage of the soul with Christ as a journey through what she called The Interior Castle.

She sees the soul as a magnificent castle full of spacious and well-lit rooms or mansions each of which leads deeper into the heart of the castle to the seat of the King. However, St. Teresa laments that most people give all their attention to the outer wall of the castle the body ignoring the beauty of the soul within.

St. Teresa gives practical advice regarding the early struggles and the temptations to turn back which beset the beginner. She describes each of the seven mansions and urges us forward to love and serve the Divine Majesty, imparting her absolute conviction that progress toward God through prayer is worth vastly more than all the treasures of this earth.

St. Teresa of Avila was born in 1515 at Avila, Spain, and her mother Beatriz was determined to bring her up as a good Christian. She attempted to find martyrdom by running away from home when she was seven, but was promptly stopped by her uncle. She later became a Carmelite nun and began to experience, while suffering from sickness, spiritual ecstasy as a result of reading Francisco de Osuna's Third Spiritual Alphabet. In 1599 she was convinced that she was actually seeing visions of Christ, which continued often for two years. Teresa of Avila founded a good many convents, including at Andalusia, Palencia and Soria. She is also the author of The Interior Castle, The Way of Perfection, and an Autobiography. She died in 1582 at the age of 67, and was canonized by Pope Gregory XV in 1622. Her feast is celebrated on October 15.