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