John, this great spiritual father, was born in Rome of renowned parents. In his youth he studied all the secular sciences, especially philosophy and astronomy. Afterward he devoted himself completely to the study of Holy Scripture. Striving to go from good to better and desiring even higher levels of perfection, Cassian traveled from Rome to Constantinople to personally hear and see St. John Chrysostom. Chrysostom instructed him and ordained him a deacon. Benefiting much from the wise Chrysostom, Cassian traveled farther east, to learn even more and achieve greater perfection. He remained in Egypt, spending the longest time in Nitria among the famous spiritual athletes, from whom he learned the art of every virtue. He finally returned to the West and settled in the town of Marseilles. There he established two monastic communities — one for men and one for women. At the request of the monks, Cassian wrote many essays. Especially beneficial for lovers of the spiritual life is his work, “Eight Books on the Struggle Against the Eight Principle Passions” (The Institutes of the Monastic Life). Of great importance is his essay against the heretic Nestorius. This essay was written at the request of Archdeacon Leo. He served our Lord faithfully and enriched many with his wisdom, then took up his habitation in eternal life in the year 435. The relics of St. John lie in Marseilles even to this day.
Source: St. Nikolai Velimirovic, The Prologue of Ohrid – Volume One.
Apolytikion
The image of God, was faithfully preserved in you, O Father. For you took up the Cross and followed Christ. By Your actions you taught us to look beyond the flesh for it passes, rather to be concerned about the soul which is immortal. Wherefore, O Holy John Cassian, your soul rejoices with the angels.