Teresa, or THERESA, ST, one of the most remarkable of the women saints of the modern Roman calendar, was born at Avila, in Old Castile, March 28, 1515, of the noble house of Cepeda. Even as a child she was remarkable for piety of a most enthusiastic kind; and, educated in a convent in her native city, she entered a convent of the Carmelite order there in 1534. In this convent she continued to reside for nearly thirty years, but it was not till about the year 1539 that her constitution became strong enough to permit her to follow, even in an imperfect way, the observances of conventual life. Her own account of her mental and spiritual condition is interesting from the first; but it was not till 1555 that a change of heart and of purpose came, which was as complete and decisive as her former condition had been purposeless or fluctuating. After a time her religious exercises reached a most extraordinary degree of asceticism. Her prayers were almost continual, and she was reported to be favoured with visions, ecstasies, and other supernatural visitations. The fame of her sanctity spread not only throughout Spain, but into almost every part of the church. By some the reality of the reported supernatural favours which were ascribed to her was called in question; and there were even some who threatened to invoke the rigorous investigation of the Holy Office; but the popular voice was freely accorded to her, and the authority of St Francis Borgia, St Peter of Alcantara, and other influential churchmen eventually disarmed the opposition. The most notable and permanent fruit of the enthusiastic spirituality of Teresa is the reform of the Carmelite order, of which she became the instrument. She commenced this work in concert with a few zealous members of her own sisterhood in the convent at Avila, where she had resided from the date of her profession; but after a time she obtained permission from the holy see to remove with her little community to a humble house in the same city, where she re-established in its full rigour the ancient Carmelite rule, as approved by Innocent IV. in 1247, with some additional observances introduced by herself. This new convent of St Joseph's was established in 1562, in which year she assumed the name of Teresa de Jesús; and in 1565 she obtained from the pope, Pius IV., a formal approval for the rule as modified by her. For two years Teresa lived in great privacy and quiet in her convent; but in 1567 the general of the Carmelite order, F. Rubeo, was so struck, during his visitation of the convents at Avila, with the condition of that over which Teresa presided that he urged upon her the duty of extending throughout the order the reforms thus successfully initiated. Teresa entered upon the work with great energy, and although she met with much opposition, nevertheless succeeded in carrying out her reforms. In 1579 the Carmelites of the stricter observance established by Teresa were released from the jurisdiction of the old superiors, and united into a distinct association, with a separate head and a distinct organisation, which was approved in 1580 by Pope Gregory XIII. Under this new constitution the association flourished and extended; and within her own lifetime no fewer than seventeen convents of women and sixteen of men accepted the reforms which she had originated. Teresa died at Alba, October 4, 1582, in her sixty-eighth year. She was canonised by Gregory XV. in 1622, her feast being fixed on the 15th October.
She left a number of works, which have at all times maintained a high reputation among a large section of her own church; their merits are also acknowledged by non-Catholic writers. They consist of ascetical and mystical treatises, instructions in the conventual life, meditations, besides a large number of letters which possess remarkable literary merit. The best-known treatises are her autobiography, The Way of Perfection, The Book of the Foundations (trans. by Dalton, 1853), and The Interior Castle (trans. by Dalton, 1852). Her works in the original Spanish fill two folio volumes (Salamanca, 1587), and they have been in whole or in part translated into almost every European language. Migne issued a French edition in 4 vols. (1840-46). Her life occupies nearly an entire volume of the Acta Sanctorum; and several biographies have been written in Spanish (Ribera's appeared in 1690), French, Italian, German—the best-known English ones being that by Canon Dalton (1851), one edited by Cardinal Manning (1865), one by Miss Trench (1875), one by Father Coleridge (3 vols. 1881-88), and Mrs Cunningham Graham's Santa Teresa (1894).