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.