St. Teresa, the foundress of the Discalced Carmelites, was born at Avila in Spain, 1515. She was called to reform her Order, favored with distinct commands from Our Lord, and her heart was pierced with divine love; but dreading delusion she acted only under obedience to her confessors, which made her strong and safe. Her heavenly Spouse called her to Himself, October 4, 1582. By the alteration of the calendar, then taking place, the next day was reckoned the fifteenth of the month, and in due course was assigned for the keeping of the feast. In the Collect we have the only example in the whole Liturgy of a reference to a woman entrusted with the office of teaching and feeding the faithful.

(Source: The New Roman Missal, Rev. F. X. Lasance)