We honor God by venerating his holy ones

Whenever, then, you see Christians adoring the Cross, know that they are adoring the Crucified Christ, not the mere wood.* If, indeed, they honoured wood as wood, they would be bound to worship trees of whatever kind, as you, O Israel, worshipped them of old, saying to the tree and to the stone, “Thou art my God and didst bring me forth.” (Jer. 2.27) We do not speak either to the Cross or to the representations of the saints in this way. They are not our gods, but books which lie open and are venerated in churches in order to remind us of God and to lead us to worship Him. He who honours the martyr honours God, to whom the martyr bore testimony. He who worships the apostle of Christ worships Him who sent the apostle. He who falls at the feet of Christ’s mother most certainly shows honour to her Son.

St. John Damascene
Apology Against Those Who Decry Holy Images
Quoted from Leo of Neapolis, Against the Jews

We worship Christ through venerating the Cross

If you, O Jew, reproach me saying that I adore the wood of the Cross as God, why do you not reproach Jacob, who worshipped on the point of his staff? Now it is evident that he was not worshipping wood. So with us; we are worshipping Christ through the Cross, not the wood of the Cross.

St. John Damascene
Apology Against Those Who Decry Holy Images
Quoted from Leo of Neapolis, Against the  Jews

Our honor of the icon is honor to the original

The image of the King is also called the king, and there are not two kings in consequence. Neither is power divided, nor is glory distributed. just as the reigning power over us is one, so is our homage one, not many, and the honor given to the image reaches back to the original. What the image is in the one case as a representation, that the Son is by His humanity, and as in art likeness is according to form, so in the divine and incommensurable nature union is effected in the indwelling Godhead.

St. John Damascene
Apology Against Those Who Decry Holy Images
Quoted from Amphilochios, On the Holy Spirit

The images of the Saints are honored in the Church

We depict Christ as our King and Lord, and do not deprive Him of His army. The saints constitute the Lord’s army. Let the earthly king dismiss his army before he gives up his King and Lord. Let him put off the purple before he takes honor away from his most valiant men who have conquered their passions. For if the saints are heirs of God, and co-heirs of Christ, (Rom. 8.17) they will be also partakers of the divine glory of sovereignty. If the friends of God have had a part in the sufferings of Christ, how shall they not receive a share of His glory even on earth? “I call you not servants,” our Lord says, “you are my friends.” (Jn. 15.15) Should we then deprive them of the honor given to them by the Church?

St. John Damascene
Apology Against Those Who Decry Holy Images
Part I

God worked out our salvation through matter

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 honoring that matter which works my salvation.

St. John Damascene
Apology Against Those Who Decry Holy Images
Part I

The Cherubim on the Ark were images commanded by God

Answer me this question. Is there only one God? You answer, “Yes, there is only one Law-giver.” Why, then, does He command contrary things? The cherubim are not outside of creation; why, then, does He allow cherubim carved by the hand of man to overshadow the mercy-scat? Is it not evident that as it is impossible to make an image of God, who is uncircumscribed and impassible, or of one like to God, creation should not be worshipped as God. He allows the image of the cherubim who are circumscribed, and prostrate in adoration before the divine throne, to be made, and thus prostrate to overshadow the mercy-seat. It was fitting that the image of the heavenly choirs should overshadow the divine mysteries.

St. John Damascene
Apology Against Those Who Decry Holy Images
Part I

There is a difference between worship and veneration

When the Invisible One becomes visible to flesh, you may then draw a likeness of His form. When He who is a pure spirit, without form or limit, immeasurable in the boundlessness of His own nature, existing as God, takes upon Himself the form of a servant in substance and in stature, and a body of flesh, then you may draw His likeness, and show it to anyone willing to contemplate it. Depict His ineffable condescension, His virginal birth, His baptism in the Jordan, His transfiguration on Thabor, His all-powerful sufferings, His death and miracles, the proofs of His Godhead, the deeds which He worked in the flesh through divine power, His saving Cross, His Sepulchre, and resurrection, and ascent into heaven. Give to it all the endurance of engraving and color. Have no fear or anxiety; worship is not all of the same kind. Abraham worshipped the sons of Emmor, impious men in ignorance of God, when he bought the double cave for a tomb. (Gen. 23.7; Acts 7.16) Jacob worshipped his brother Esau and Pharaoh, the Egyptian, but on the point of his staff.* (Gen 33.3) He worshipped, he did not adore. Joshua and Daniel worshipped an angel of God; (Jos. 5.14) they did not adore him. The worship of latreia is one thing, and the worship which is given to merit another.

St. John Damascene
Apology Against Those Who Decry Holy Images
Part I