It was while she was in the convent that her religious experiences began. In 1554 she had a deeper conversion when she saw a statue of Jesus after he had been whipped. She was deeply moved and wrote, “I felt so keenly aware of how poorly I had thanked him for those wounds that, it seems to me, my heart broke. I threw myself down before him with the greatest outpouring of heart.” After this experience she progressed into a life of intense prayer and the Catholic practice of mortification, so much so that he motto became, "Lord, either let me suffer or let me die." She was also deeply influenced by the Confessions of Augustine and other theological books – although she did not have access to the Bible. Perhaps the single most influential experience she had was when she ‘came back from the dead’ after suffering from what is thought to have been malaria. This increased her notoriety.
Moving on, Teresa was encouraged to write about her experiences and her books continue to influence mysticism today. Her two main writings are Way of Perfection and The Interior Castle. Way of Perfection is considered her spiritual autobiography. Here she emphasises the importance of praying mentally as well as vocally. In sixteenth century Spain the common people were encouraged to restrict themselves to vain repetitions of learned-off prayers, Teresa rejected this in favour of a more personal relationship with God. Her superbly inspiring classic on the practice of prayer is as fresh and meaningful today as it was when she first wrote it. The Way of Perfection is a practical guide to prayer setting forth the Saint's counsels and directives for the attainment of spiritual perfection. Through the entire work there runs the author's desire to teach a deep and lasting love of prayer beginning with a treatment of the three essentials of the prayer-filled life -- fraternal love, detachment from created things, and true humility. St. Teresa's counsels on these are not only the fruit of lofty mental speculation, but of mature practical experience.
In The Interior Castle she compares the soul to a castle with seven rooms, with the Trinitarian God residing in the inner room. Growth in prayer enables the believer to reach a deeper intimacy with God, symbolised by a progressive journey through the rooms of the castle. She also describes the resistance that the Devil places in various rooms, to keep believers from union with God. Throughout, she provides encouragements and advice for spiritual development. Teresa’s writings lack Biblical references due to the Spanish Inquisition restricting access to the scriptures, and this grieved her.
William James identified four characteristics of religious experience: ineffability; noetic quality; transiency and passivity. All of these care clearly apparent with Teresa’s experiences. Starting with ineffability, this is when one experiences a feeling that cannot be described to anyone else. She wrote that, “the soul is fully awake as regards God, but wholly asleep as regards the things of this world.” Secondly, noetic quality is when the mystic experience gives insight into truths unobtainable by the intellect alone. This is also apparent in Theresa’s experiences: “when I return to myself, it is wholly impossible for me to doubt that I have been in God, and God in me.” Thirdly, transiency. The religious experience does not last for long, usually half an hour or so. Though they are remembered, they are imperfectly recalled, but recognised if they reoccur – the recipient usually feels a profound sense of the importance of the experience. Associated with Teresa’s raptures are always visions. Her most famous vision involved her seeing a small angel with a beautiful face holding “a long golden spear” tipped with a “little fire” which he thrust into her heart. Finally, there is passivity, when the mystic feels as if they have been taken over by a superior power. In Teresa’s case, her visions were sometimes accompanied by levitation or strange screams. It could be this aspect that led many to believe she was possessed by the devil.
In terms of impact, Teresa of Avila had a profound influence on religious experience. She the first female saint of the Roman Catholic Church – the saint of headache sufferers, rather oddly. She was somewhat of a reformer, emphasising a personal relationship with God above rigid sacramentalism. In 1562 she established the strict Carmelite order in various areas of Spain and her writings continue to be studied by believers today.