Isidore was Egyptian by birth and from a prominent Alexandrian family, which included Alexandrian Patriarchs [[Theophilus of Alexandria|
Theophilos]] and [[Cyril of Alexandria|Cyril]]. He studied all the secular disciplines, but as a youth withdrew from the world, renouncing his riches and earthly glory, so that he might devote himself entirely to the spiritual life. For a short time he taught rhetoric in Pelusium in Egypt; but soon his love for the things of God led him to flee to the desert as a solitary. After a year of [[asceticism|ascetical]] life, he returned to Pelusium, where he was ordained to the [[priest]]hood. After a few years he retired to a monastery where he spent the rest of his life, eventually becoming [[abbot]]. From the monastery he wrote thousands of epistles full of divine grace and wisdom; of these more than two thousand still survive.
During his lifetime, he came to be a great and energetic defender of the Orthodox Christian faith, writing (according to the historian Nicephorus) more than ten thousand letters to numerous individuals, giving reproach, counsel, encouragement, comfort, and instruction.