I read in it the wild conceptions of a Spanish nun, devout to superstition, melancholy, shut in by convent walls, and swayed by the ignorance and bigotry of her confessors.  All these grotesque, monstrous, and fantastic visions of hers were dignified with the name of revelations.  The lover and bosom-friend of the Holy Virgin, she had received instructions from God Himself to write the life of His divine mother; the necessary information was furnished her by the Holy Ghost.

This life of Mary began, not with the day of her birth, but with her immaculate conception in the womb of Anne, her mother.  This Sister Mary of Agrada was the head of a Franciscan convent founded by herself in her own house.  After telling in detail all the deeds of her divine heroine whilst in her mother’s womb, she informs us that at the age of three she swept and cleansed the house with the assistance of nine hundred servants, all of whom were angels whom God had placed at her disposal, under the command of Michael, who came and went between God and herself to conduct their mutual correspondence.

What strikes the judicious reader of the book is the evident belief of the more than fanatical writer that nothing is due to her invention; everything is told in good faith and with full belief.  The work contains the dreams of a visionary, who, without vanity but inebriated with the idea of God, thinks to reveal only the inspirations of the Divine Spirit.

The book was published with the permission of the very holy and very horrible Inquisition.  I could not recover from my astonishment!  Far from its stirring up in my breast a holy and simple zeal of religion, it inclined me to treat all the mystical dogmas of the Faith as fabulous.

Such works may have dangerous results; for example, a more susceptible reader than myself, or one more inclined to believe in the marvellous, runs the risk of becoming as great a visionary as the poor nun herself.

The need of doing something made me spend a week over this masterpiece of madness, the product of a hyper-exalted brain.  I took care to say nothing to the gaoler about this fine work, but I began to feel the effects of reading it.  As soon as I went off to sleep I experienced the disease which Sister Mary of Agrada had communicated to my mind weakened by melancholy, want of proper nourishment and exercise, bad air, and the horrible uncertainty of my fate.  The wildness of my dreams made me laugh when I recalled them in my waking moments.  If I had possessed the necessary materials I would have written my visions down, and I might possibly have produced in my cell a still madder work than the one chosen with such insight by Cavalli.

This set me thinking how mistaken is the opinion which makes human intellect an absolute force; it is merely relative, and he who studies himself carefully will find only weakness.  I perceived that though men rarely become mad, still such an event is well within the bounds of possibility, for our reasoning faculties are like powder, which, though it catches fire easily, will never catch fire at all without a spark.  The book of the Spanish nun has all the properties necessary to make a man crack-brained; but for the poison to take effect he must be isolated, put under the Leads, and deprived of all other employments.