Solomon’s temple, like the Church, was decorated by images

The temple which Solomon built was consecrated by the blood of animals, and decorated by images of lions, oxen, and the palms and pomegranates. Now, the Church is consecrated by the blood of Christ and of His saints, and it is adorned with the image of Christ and of His saints.

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

The Saints are deserving of honor

For if the friends of Christ are heirs of God and co-heirs of Christ, and are to be partakers of the divine glory and kingdom, is not even earthly glory due to them? I call you not servants, our Lord says; you are my friends. Shall we, then, withhold from them the honor which the Church gives them?

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

Iconoclasm requires one to follow the whole law, and therefore fall from grace

If you give up images on account of the law, you should also keep the Sabbath and be circumcised, for these are severely inculcated by it…But you must know that if you observe the law, Christ will profit you nothing.

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

The Lord worked out our salvation through matter

It is not matter which I adore; it is the Lord of matter, becoming matter for my sake, taking up His abode in matter and working out my salvation through matter. For “the Word was made Flesh, and dwelt amongst us.” (Jn. 1.14) It is evident to all that flesh is matter, and that it is created. I reverence and honour matter, and worship that which has brought about my salvation. I honour it, not as God, but as a channel of divine strength and grace.

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

Fidelity to Church tradition, even in the slightest thing, is critical

We are obedient to you, O King, in things concerning our daily life, in tributes, taxes, and payments, which are your due; but in ecclesiastical government we have our pastors, preachers of the word, and exponents of ecclesiastical law. We do not change the boundaries marked out by our fathers (Prov. 22.28): we keep the tradition we have received. If we begin to lay down the law to the Church, even in the smallest thing, the whole edifice will fall to the ground in no short time.

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

The intention of those who venerate is what’s important

So with regard to images we must manifest the truth, and take into account the intention of those who make them. If it be in very deed for the glory of God and of His saints to promote goodness, to avoid evil, and save souls, we should receive and honour and worship them as images, and remembrances, likenesses, and the books of the illiterate. We should love and embrace them with hand and heart as reminders of the incarnate God, or His Mother, or of the saints, the participators in the sufferings and the glory of Christ, the conquerors and overthrowers of Satan, and diabolical fraud. If any one should dare to make an image of Almighty God, who is pure Spirit, invisible, uncircumscribed, we reject it as a falsehood. If any one make images for the honour and worship of the Devil and his angels, we abhor them and deliver them to the flames. Or if any one give divine honours to the statues of men, or birds, or reptiles, or any other created thing, we anathematise him.

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

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