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

Epiphanius is falsely attributed to rejecting icons

If, again, you object that the great Epiphanius thoroughly rejected images, I would say in the first place the work in question is fictitious and unauthentic. It bears the name of some one who did not write it, which used to be commonly done. Secondly, we know that blessed Athanasius objected to the bodies of saints being put into chests, and that he preferred their burial in the ground, wishing to set at nought the strange custom of the Egyptians, who did not bury their dead under ground, but set them upon beds and couches. Thus, supposing that he really wrote this work, the great Epiphanius, wishing to correct something of the same kind, ordered that images should not be used. The proof that he did not object to images, is to be found in his own church, which is adorned with images to this day. Thirdly, the exception is not a law to the Church, neither does one swallow make summer, as it seems to Gregory the theologian, and to the truth. Neither can one expression overturn the tradition of the whole Church which is spread throughout the world.

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

Unwritten traditions are handed down in the Church

How do we know the Holy place of Calvary, or the Holy Sepulchre? Does it not rest on a tradition handed down from father to son? It is written that our Lord was crucified on Calvary, and buried in a tomb, which Joseph hewed out of the rock; (Mt. 27.60) but it is unwritten tradition which identifies these spots, and does more things of the same kind. Whence come the three immersions at baptism, praying with face turned towards the east, and the tradition of the mysteries?* Hence St Paul says, “Therefore, brethren, stand fast, and hold the traditions which you have learned either by word, or by our epistle.” (II Thess. 2.15) As, then, so much has been handed down in the Church, and is observed down to the present day, why disparage images?

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

The relics of the Apostles were miraculous so shouldn’t the Saints be glorified?

…the image of Him who is visible to flesh is burnt into my soul. The shadow and winding sheet and relics of the apostles cured sickness, and put demons to flight. (Acts 5.15) How, then, shall not the shadow and the statues of the saints be glorified?

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

Christ has deified our flesh

From the time that God the Word became flesh He is as we are in everything except sin, and of our nature, without confusion. He has deified our flesh for ever, and we are in very deed sanctified through His Godhead and the union of His flesh with it.

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

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

The Temple of Solomon was covered with images

God charged David to build Him a temple through his son, and to prepare a place of rest. Solomon, in building the temple, made the cherubim, as the book of Kings says. And he encompassed the cherubim with gold, and all the walls in a circle, and he had the cherubim carved, and palms inside and out, in a circle, not from the sides, be it observed. And there were bulls and lions and pomegranates. (I Kgs. 6.28-29) Is it not more seemly to decorate all the walls of the Lord’s house with holy forms and images rather than with beasts and plants? Where is the law declaring “thou shalt not make any graven image”?

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

Christ’s flesh was unchangeably also God

St John, who rested on His breast, says, that “we shall be like to Him” (I Jn. 3.2): just as a man by contact with fire becomes fire, not by nature, but by contact and by burning and by participation, so is it, I apprehend, with the flesh of the Crucified Son of God. That flesh, by participation through union with the divine nature, was unchangeably God, not in virtue of grace from God as was the case with each of the prophets, but by the presence of the Fountain Head Himself.

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