The Mystical City of God is an exceptionally great work of historical significance. This becomes apparent from the official action taken by a number of Popes, all indirectly approving of the work and promoting its publication. Pope Innocent XI and Pope Alexander VIII in 1690 expressly declared that the City of God may be read by all the faithful. Pope Clement XI and Benedict XIV gave like decisions. The great pope Benedict XIII, when he was archbishop of Benevent, used these revelations as material for a series of sermons on the Blessed Virgin.
Numerous popes, cardinals and theologians have praised this work over a period of more than 300 years. The learned and pious Cardinal D'Aguirre says that he considers all the studies of fifty years of his life as of small consequence in comparison with the doctrines he found in this book, which in all things are in harmony with the Holy Scriptures, the Holy Fathers and Councils of the Church. The Venerable Superior-General of St. Sulpice, Abbe' Emery, adds: "Only since I read the revelations of Mary of Agreda do I properly know Jesus and his Holy Mother."
Book One, named The Conception deals with the Sacramental Mysteries wrought by the Most High in the Queen of Heaven from the Time of her Immaculate Conception until the Incarnation of the Word in her virginal Womb, and how much Merit She herself acquired through divine Grace by profiting from the favors conferred upon Her during those first fifteen Years of her Life.
Book Two, named The Incarnation deals with the Mysteries of the Life of the Holy Mother of God from the Incarnation of the Divine Word in her virginal Womb to the Return of the Holy family from Egypt.
Book Three, named The Transfixion deals with the Sacramental Mysteries of the life of the Mother of God from the return out of Egypt up to her divine Son's Ascension into heaven.
Book Four, named The Coronation deals with the heavenly Life of the Queen of Heaven, most holy Mary, containing the Events of her Life from the Coming of the Holy Ghost until the Assumption and Coronation of the Virgin Mother of God in Heaven.
There are four books in the set, totaling 2793 pages.