John Cassian had come very late into writing and only does so when a request is made by an important person or persons.
His sources are the same as those of Evagrius Ponticus, who had been among his teachers, but he adds his own personal ideas, which are arranged in extensive collections.
Cassian writes two major spiritual works, the Institutions and the Conferences.
In these, he codifies and transmits the wisdom of the Desert Fathers of Egypt.
These books are written at the request of Castor, Bishop of Apt, of the subsequent Pope Leo I, and of several Gallic bishops and monks.
The Institutions (Latin: De institutis coenobiorum) deal with the external organization of monastic communities, while the Conferences (Latin: Collationes patrum in scetica eremo) deal with "the training of the inner man and the perfection of the heart."
In Books 1-4 of Institutions, Cassian discusses clothing, prayer and rules of monastic life.
Books 5-12 are rules on morality, specifically addressing the eight vices - gluttony, lust, avarice, hubris, wrath, envy, acedia, and boasting - and what to do to cure these vices.
The Conferences, dedicated to Pope Leo, to the bishop of Frejus, and to the monk Helladius, summarize important conversations that Cassian had had with elders from Scetis about principles of the spiritual and ascetic life.
This book addresses specific problems of spiritual theology and the ascetic life.
It will later be read in Benedictine communities before a light meal, and from the Latin title, Collationes, comes the word collation in the sense of "light meal."
His third book, On the Incarnation of the Lord, is a defense of orthodox doctrine against the views of Nestorius, and is written at the request of the Archdeacon of Rome, later Pope Leo I.
His books, written in Latin, in a simple, direct style, are swiftly translated into Greek, for the use of Eastern monks, an unusual honor.
He dies in the year 435 in Marseille.
John Cassian's abbey and writings will influence St. Benedict, who will incorporate many of the same principles into his monastic rule (Rule of St. Benedict), and recommend to his own monks that they read the works of Cassian.
(Since Benedict's rule is still used by Benedictine, Cistercian, and Trappist monks, the thought of John Cassian still guides the spiritual lives of thousands of men and women in the Western Church.)
