When she was about 20 years old she entered the Carmelite convent. Her life in the convent did not change much, because she was not bound to follow any rules and when she had friends visit, they were never bored.
Sometime between entering the convent and turning 40, she started to feel that God was disappointed by the way she was conducting her life and her worldly belongings started to disturb her as well.
In 1555, when she was 40 she stared at a painting of the Passion of Christ displayed for an upcoming feast at the convent and this gave her the feeling of truly understanding Christ's suffering. She then threw herself down and felt that all vain and worldly ambitions died inside of her. After that she made more time for prayer, she was different from the way she was that the others in the convent thought she was mislead by the devil.
St. Teresa then went to the Jesuits for spiritual direction. They gave her a more thorough penance, and this did not help with her visions that were getting more dramatic.
The most famous vision was, the Transverberation of the Heart, during which St. Teresa saw an Angel with a golden spear tipped with fire, which was then driven again and again into her heart. She described it as "an imaginary vision seen by the eyes of the soul." The pain she felt was very real and lasted several days.
That summer on July 16, the feast day of Our Lady of Mount Carmel, St. Teresa and her closest friends gathered in her cell and decided they would need a house for them to be able to truly follow the original Carmelite Rule: sleeping on straw, fasting eight months a year, abstaining from meat and living in total seclusion. They went barefoot, and that is where the name Discaled Carmelites came from. The other nuns criticized her and refused to recognize St. Teresa's new Foundation.
The bishop on the other hand thought this would reinvigorate the Church and encouraged her to travel all over Spain and establish new foundations and reforming existing ones.
In Toledo (Spain), she was placed under house arrest for two years and while under arrest she wrote books. Her autobiography and "The Interior Castle" and "The Way of Perfection."
She died in the arms of Anne of St. Bartholomew on October 4, 1582 in Alba de Tormes in Spain.
Her incorrupt body is adored in Alba de Tormes, Spain. Pilgrims can come and see her heart; it still bears the mark where the angel pierced it with its golden arrow.
She was beatified in 1614 and canonized in 1622 by Pope Gregory XV (15th) and in 1970 was made a Doctor of the Church.