Of old, God the incorporeal and uncircumscribed was never depicted. Now, however, when God is seen clothed in flesh, and conversing with men, (Bar. 3.38) I make an image of the God whom I see. I do not worship matter, I worship the God of matter, who became matter for my sake, and deigned to inhabit matter, who worked out my salvation through matter. I will not cease from honouring that matter which works my salvation. I venerate it, though not as God. How could God be born out of lifeless things? And if God’s body is God by union (καθ υποστασιν), it is immutable.
The nature of God remains the same as before, the flesh created in time is quickened by a logical and reasoning soul. I honour all matter besides, and venerate it. Through it, filled, as it were, with a divine power and grace, my salvation has come to me. Was not the thrice happy and thrice blessed wood of the Cross matter? Was not the sacred and holy mountain of Calvary matter? What of the life-giving rock, the Holy Sepulchre, the source of our resurrection: was it not matter? Is not the most holy book of the Gospels matter? Is not the blessed table matter which gives us the Bread of Life? Are not the gold and silver matter, out of which crosses and altar-plate and chalices are made? And before all these things, is not the body and blood of our Lord matter?
Either do away with the veneration and worship due to all these things, or submit to the tradition of the Church in the worship of images, honouring God and His friends, and following in this the grace of the Holy Spirit.Do not despise matter, for it is not despicable. Nothing is that which God has made. This is the Manichean heresy. That alone is despicable which does not come from God, but is our own invention, the spontaneous choice of will to disregard the natural law,—that is to say, sin.
Excerpt from Apologia of St John of Damascus Against Those who Decry Holy Images