John of Damascus

John's family were Christians of Damascus who served the administration, first Byzantine and then Umayyad, and he appears to have held a financial post under the caliph before withdrawing to the monastery of Mar Saba in the Judaean desert. That biography is the key to his position. When the emperors in Constantinople began suppressing the veneration of images in the 720s, the most effective theological opposition came from a monk living outside their jurisdiction, in a territory the emperor could not reach.

His major work, the Fount of Knowledge, is in three parts: a philosophical vocabulary, a catalogue of heresies, and the Exact Exposition of the Orthodox Faith, which sets out the whole of Christian doctrine in order. It is the first systematic summa in the Greek tradition, it was translated into Latin in the twelfth century and used by the western scholastics, and it remains a standard reference in Orthodox theology. He was explicit that he was not being original: he described himself as gathering what the fathers had said, and that self-effacement is part of why the book was trusted.

The catalogue of heresies contains what is generally taken to be the earliest Christian discussion of Islam, written by a man who had grown up under Muslim rule and knew the Quran at first hand. He treats it as a Christian heresy rather than a separate religion, which is how the Greek world classified it for centuries afterwards.

The three treatises John wrote against the iconoclasts make an argument that the Second Council of Nicaea eventually adopted almost intact, and it turns on two distinctions.

The first is about words. Greek has more than one term for the reverence given to something, and John insists on separating them: latreia, adoration, is due to God alone and to nothing else whatever, while proskynesis, the honour of bowing before something, is given to many things, to rulers, to the gospel book, to parents. Honouring an image is the second and never the first, and the honour passes to the one depicted rather than resting on the wood.

The second is about matter, and it is the theological heart of it. The Old Testament prohibition applies to depicting a God who has never been seen. That situation changed at the incarnation, when the invisible God took flesh and became visible; to refuse to depict him is therefore to be embarrassed by the incarnation. John puts it directly: he does not worship matter, he says, but he worships the God of matter, who became matter for his sake and worked salvation through matter.

The iconoclast council of Hieria in 754 anathematised him by name. Thirty three years later the Second Council of Nicaea reversed the anathema and endorsed his theology. He is also a substantial hymnographer, and material attributed to him remains in the Byzantine liturgical books.