The theological argument for icons was forced into its sharpest form by a state campaign to destroy them. Beginning around 726, Byzantine emperor Leo III moved against the veneration of images, and his son Constantine V convened a council in 754 that condemned icons outright, on the grounds that any image of Christ either falsely confined his divine nature to paint or falsely divided his two natures by depicting only the human one. Soldiers whitewashed church walls, burned panel icons and in some accounts destroyed relics along with them, and monks, who were prominent icon defenders, were harassed and in places killed.
John of Damascus, writing from safety outside imperial territory, supplied the counterargument that later prevailed: since God took a visible, circumscribable human body in the incarnation, refusing to depict Christ denied that the incarnation had truly happened, and honour shown to an image passes to its prototype rather than terminating in wood and paint. The Second Council of Nicaea restored icons in 787, a second wave of destruction followed under later emperors, and the controversy was finally settled in 843, an event still kept in the Orthodox calendar as the Feast of Orthodoxy, the first Sunday of Great Lent, celebrated precisely as the restoration of the icons. The episode left a permanent mark on Orthodox self-understanding: icon veneration is remembered not as an inherited custom that went unquestioned but as a position fought for and defined against an explicit doctrinal rival, which is why Orthodox writers describe the practice in credal terms rather than merely devotional ones.