“The eternal law of righteousness ordains that he who will not submit to God's sweet rule shall suffer the bitter tyranny of self: but he who wears the easy yoke and light burden of love (Matthew 11:30) will escape the intolerable weight of his own self-will.” Bernard of Clairvaux ultimately incorporated these words into his treatise On Loving God, but they were originally part of a letter sent to a group of Carthusians. Since the Carthusians belonged to one of the most austere religious orders of the day, these monks might have had a special need for the saint's reminder that the tyranny of self-will exacted an even heavier toll than did the burdens imposed upon them by their monastic rule. But while religious in other orders did not subject themselves to anything like Carthusian rigors (the customs and constitutions of specific orders were not uniform; nor were requirements for male and female religious, even those belonging to the same order, identical), all would have needed encouragement to persevere in a vocation from which death alone afforded a legitimate escape. For medieval canon law insisted that monastic vows, taken freely, were never to be freely abandoned; as the Glossa Ordinaria, the standard commentary on medieval canon law, put it, “To make a vow is a matter of the will; to fulfill one is a matter of necessity.”

Most, but not all, of the nuns treated in this book satisfied the first of these canonical dictates: They had professed their vows willingly and in so doing had created a legally binding commitment to the monastic life. They then failed, however, to fulfill that commitment. By virtue of leaving their religious houses and reentering secular society they became apostates, and although their motives were nearly as various as the individuals involved, the very act of abandoning the religious life gave them this uniform legal status.

As the lay man or woman became an apostate by rejecting the Christian faith subsequent to baptism, so medieval religious became apostates when they rejected their freely chosen vowed life subsequent to formal profession. By the end of the thirteenth century, the point at which this study begins, the developed canon law had established some clear juridical standards when dealing with apostates.