An icon is a symbol of the invisible. It depicts not only the outward, visible countenance of the Lord and His saints, but also their inner likeness, their sanctity.
St. John Climacus was asked if there are reliable signs by which it's possible to know whether a soul is drawing near to God or moving away from Him. After all, regarding ordinary things there are clear signs as to whether they're good or not. When, for instance, cabbage, meat or fish begins to rot, it's easy to notice it, since the rotting object begins to give off a foul odor, the color and taste change, and its external appearance witnesses to its deterioration. Well, and what about the soul? After all, it's bodiless and can't give off a bad smell or change its appearance. To this question the Holy Father replies, 'A sure sign of the deadening of the soul is the avoidance of church services.'
When the blessed Eulogius saw an angel distributing gifts to the monks who toiled at all-night vigils, to one he gave a gold piece with the image of Our Lord Jesus Christ, to another a silver piece with a cross, to another a copper piece, to another a bronze piece, and to another nothing. The others who had remained in the church, left the church empty-handed. It was revealed to him that the ones who had obtained the gifts are those who toil at vigils and are diligent in prayers, supplications, psalms, chants, and readings. Those who received nothing or who left the church empty-handed are those who are heedless of their salvation, are enslaved to vainglory and the clamors of life, and stand feebly and lazily at vigils and whisper and jest.
If you speak of pagan abuses, these abuses do not make our veneration of images loathsome. Blame the pagans, who made images into gods! Just because the pagans used them in a foul way, that is no reason to object to our pious practice. Sorcerers and magicians use incantations and the Church prays over catechumens; the former conjure up demons while the Church calls upon God to exorcise the demons. Pagans make images of demons which they address as gods, but we make images of God incarnate, and of His servants and friends, and with them we drive away the demonic hosts... If the Scripture says, The idols of the nations are silver and gold, the work of men's hands (Ps. 135:15), it is not forbidden to bow before inanimate things, or the handiwork of men, but only before those images which are the devil's work.
You are, I am sure, aware that for you penitence is now no longer limited to disclosing your sins to your confessor, but that you must now bear your sins in mind always, until your heart nearly breaks with their ugly load; and would break, were it not for your firm faith in the mercy of our Lord.