The Monk Isidore Pelusiot lived in the IV–V centuries. Originally from Alexandria. I grew up among pious Christians. He was related to Theophilus, Archbishop of Alexandria, and his successor, Saint Cyril. As a young man, he left the world and retired to Egypt on Mount Pelusiote, which became the site of his monastic exploits. The spiritual wisdom and strict asceticism of St. Isidore, combined with the broad enlightenment and natural knowledge of the human soul, allowed him to gain the respect and love of the monks in a short time. They elected him their superior and elevated him to the rank of presbyter. 
Following the example of St. John Chrysostom, whom he happened to see and hear during his trip to Constantinople, St. Isidore devoted himself primarily to Christian preaching, to that "practical philosophy" which, in his own words, is "the foundation of the building and the building itself," while logic "is its decoration," and "contemplation is the crown." He was a teacher and a reliable giver of advice to all who turned to him for spiritual support – whether it was a simple man, a nobleman, a bishop, the Patriarch of Alexandria or the emperor himself. He left behind about 10,000 letters, of which 2,090 have reached us. Most of these letters contain profound theological thoughts and at the same time morally edifying interpretations of the Holy Scriptures. Here St. Isidore acts as the best disciple of St. John Chrysostom. St. Isidore's love and devotion to St. John Chrysostom manifested itself in his resolute actions in defense of St. John during the persecution of Empress Eudoxia and Archbishop Theophilus. After the death of the saint, St. Isidore persuaded Theophilus' successor, St. Cyril of Alexandria, to inscribe the name of St. John Chrysostom in church diptychs as a confessor. On the initiative of St. Isidore, the Third Ecumenical Council was convened in Ephesus (431), at which Nestorius' false teaching about the Person of Jesus Christ was condemned.
Saint Isidore reached a great old age and died around the year 436. The church historian Evagrius (VI century) writes about St. Isidore that "his life seemed to everyone like an angelic life on earth." Another historian, Nikephoros Kallistos (XI century), praises St. Isidore in this way: "He was a living and animated pillar of monastic rules and Divine vision, and, as it were, the highest example of the warmest imitation and spiritual teaching."