The Second Nun begins her tale with a prologue in which she explains the value of work and the dangers of idleness ("Ydelnesse"), or sloth; offers an invocation to the Virgin Mary, asking for help in rendering accurately this tale of Cecilia; and offers an interpretation of the name Cecilia.
A noble young lady named Cecilia loves the Virgin Mary and chastity so much that she wants to remain a virgin forever. Ultimately, however, she is betrothed to a man named Valerian, and on her wedding night, she informs her new husband that a guardian angel will slay anyone who violates her body. Valerian wants to see this guardian angel but first must be baptized by Pope Urban. To this end, he is baptized by the pope; during the baptism, he witnesses a vision proclaiming the One God. Returning home to his wife, Valerian sees her guardian angel and asks that the angel grant him one wish: that his brother, Tiburse, be baptized.
Later, a vile pagan named Almachius arrests Cecilia. At the trial, the judge questions Cecilia; although she answers cleverly, she is condemned to death. She is first placed in scalding hot water but survives; next, the executioner tries three times to cut off Cecilia's head but fails. She lives for three more days, during which she sings and converts non-believers. Following her eventual death, Pope Urban decrees her to be Saint Cecilia.
Because nuns in Chaucer's time were compelled to read stories of the saints, the tale of Cecilia is an apt selection for the Second Nun simply because she is a nun and is extremely modest and shy. Her invocation to Mary is typical for all stories, but more so here because the story of St. Cecilia is a story of chastity.
The interpretation of a name was a favorite device during Chaucer's day. Although the Second Nun's interpretation is not correct from an etymological viewpoint, it includes a traditional interpretation that identifies Cecilia with the "heavenly lily for her Chaste virginity"; a road for the blind (non-Christian) by the example of her teachings; a combination of heaven and the biblical Leah who represents the active or busy life; and heaven made visible to the ordinary people.
Just as men see the sun, moon, and stars in heaven, so they see in this maiden her faith and magnanimity and also the whole clarity of her wisdom and the excellence of her works. If heaven and Cecilia are the same, then Cecilia represents the medieval Philosopher's Stone, the stone that, in alchemy, could change base metals into precious metals — a metaphor for the purification of the soul. Thus, if heaven and Cecilia are the same, Cecilia can (figuratively and spiritually) change lead into gold or pagans into Christian.
In Chaucer's day, nuns were compelled to read stories of saints, especially those stories about women who were canonized because they literally fought against horrible obstacles to retain their chastity and suffered many tortures to protect their virtue. Such might be the context that informs The Second Nun's Tale. For the Second Nun, who was versed in stories of female saints and their struggle to remain virgins, it is natural for her to present the life story of Saint Cecilia, a martyr whose life story includes forced marriage, devotion to chastity, punishment for her chastity, and a miracle.
The appeal of this type of story — a saint's tale — is often very difficult for a modern reader to appreciate. During the Middle Ages, there was a rise in what is commonly known today as the Cult of the Virgin Mary, beginning as early as the third century a.d. The cult inspired certain religious people to place an extraordinary price on chastity and virginity. A virgin was held in the highest esteem; the physical female body became an altar of chastity to be preserved in the highest manner.