Teresa Sanchez Cepeda Davila y Ahumada was born in Avila, in what is now Spain, on March 28, 1515. She was the third child of a noble Don Alonso Sanchez de Cepeda and his second wife, Doņa Beatriz, who died when Teresa was 14. Her father was a saintly and literate man, and her mother was a pious and loving. After the death of her mother she was sent to school under the Augustinian nuns in Avila but left after 18 monthe due to illness. She remained with her father and an Uncle after leaving school, and they continued her education.
Her Uncle introduced her to the writings of St. Jerome, which instilled in her the desire for the religious life, although she considered it a safe route rather than a true calling. At first her father did not give her his consent, so she left home in 1535 without telling him and entered the Carmelite Convent of the Incarnation at Avila. On seeing this determination her father relented, but leaving her family on those terms was a heart rending experience for Teresa, which she later compared to death.
A year after taking her vows Teresa became very ill, and due to inept medical treatment she was incapacitated for a lengthy period and never fully recovered her health. It was during this period of illness that she began practicing mental prayer. She was granted many 'interior locutions and visions', in which none of the 5 exterior senses are involved. She considered herself unworthy of such favors but God would increase his work in her when she resisted. Word of her visions speread through Avila and troubled the people living there, and attracted the attention of the Dominicans and Jesuits, including St. Francis Borgia, who determined her veracity and counseled her spiritually.
Teresa wrote an account of her experiences in an autobiography and in her book "The Interior Castle". She also founded 12 reform minded communities Discalced Carmelite Nuns of the Primitive Rule and four male communities, with some assistance from St. John of the Cross. She recounted the story of these in her "Book of Foundations". She faced strong opposition throughout in this work but with the help of Phillip II the Discalced Carmelite province was approved and canonically established on June 22, 1580.
Shortly afterward on Oct. 4, 1582 she passed away. Due to the reform of the calendar the following day was reckoned as October 15. Her body was transferred to Avila, but later conveyed to Alba, where it is still preserved incorrupt. Her heart, showing the marks of Transverberation, is exposed there as well. She was beatified in 1614, and canonized in 1622 by Pope Gregory XV. She was declared a Doctor of the Church in 1970. Her feast day is October 15.