What is the theme in The Interior Castle by Teresa of Avila?

The entire book contains themes of turning away from and leaving behind the priorities of earth. Prayer is the first step toward no longer trusting the world to satisfy one's soul and turning toward the eternal, which contains those things God intended to feed eternal souls. The vile creatures outside and in the exterior dwellings of the castle symbolize the appetites and material distractions of the world, all of which are temporary and without the ability to satisfy. It is the soul's responsibility to turn away from the things she recognizes as pulling her attention from her God, and to retrain her appetites to crave the things of God. Even in the deeper dwellings, closer to God, Teresa talks about the human temptation to grow prideful at observing one's progress, and reminds her readers that every good gift they receive is from God, having nothing to do with the soul's deserving it. God gives gifts out of His grace because He sees benefit in giving them.