John spent most of his life in the Monastery of Saint Sabas near Jerusalem, and all of his life under Muslim rule, indeed protected by it.
He was born in Damascus, received a classical and theological education, and followed his father in a government position under the Arabs. After a few years, he resigned and went to the Monastery of Saint Sabas.
He is famous in three areas:
First, he is known for his writings against the iconoclasts, who opposed the veneration of images. Paradoxically, it was the Eastern Christian emperor Leo who forbade the practice, and it was because John lived in Muslim territory that his enemies could not silence him.
Second, he is famous for his treatise, Exposition of the Orthodox Faith, a summary of the Greek Fathers, of which he became the last. It is said that this book is for Eastern schools what the Summa of Aquinas became for the West.
Third, he is known as a poet, one of the two greatest of the Eastern Church, the other being Romanus the Melodist. His devotion to the Blessed Mother and his sermons on her feasts are well known.
John defended the Church’s understanding of the veneration of images and explained the faith of the Church in several other controversies. For over 30 years, he combined a life of prayer with these defenses and his other writings. His holiness expressed itself in putting his literary and preaching talents at the service of the Lord.