In THE INTERIOR CASTLE the great St. Teresa of Avila presents a remarkable description of the entire spiritual life, beginning with the first step out of mortal sin into Sanctifying Grace and ending with the Mystical Marriage of the soul with Christ. But in the process she gives scores of wonderful insights on a host of spiritual topics, so that even the casual reader can easily gather up a rich harvest.
This book is actually a record of St. Teresa's own personal experience, but it harmonizes beautifully with Thomistic teaching. She saw the soul in the state of grace as huge, magnificent and spacious: "The capacity of the soul is beyond all our understanding, and the Sun within this palace [God] enlightens every part of it." Yet St. Teresa laments that most people give all their attention to the outer wall of the castle - the body - ignoring the soul within.