St. Teresa of Avila made an enormous contribution to Christians' understanding of contemplative prayer. She discovered silent, non-verbal prayer after being brought up to believe prayer required words. St. Teresa wrote many books on contemplative prayer, including The Interior Castle where she used the metaphor of a castle with many rooms to explain the different stages of contemplative prayer. The castle represented a person's interior prayer life and their journey to the innermost room where the soul can be united with God. Through her writings and metaphor of the castle, St. Teresa helped many in Christianity comprehend the nature of non-verbal contemplative prayer.