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.