Before the Incarnation, there were no images made of God. In fact, it was expressly forbidden. But because God took on flesh and became one of us, He then had a specific appearance in time and place, and thus it is permitted for us to make an icon of God as He appears in Jesus Christ. It has been said this way:
The inconceivable is conceived in the womb of a virgin.
The immeasurable became 3 cubits high; the unqualifiable acquires a quality; the undefinable stands up, sits down and lies down; He who is everywhere is put into a crib.
He who is above time gradually reaches the age of 12; He who is formless appears with the shape of a man and the incorporeal enters into a body.
Therefore, the same is describable and indescribable.
—from the writings of the Desert Fathers: St. Theodore the Studite
Every icon is an icon of Christ. Sometimes that is obvious, as in this icon of Christ the Savior.
Many icons depict a saint. Saints have been transfigured by grace, and God dwells in the temple of their souls.
Their lives were lived through Him, and with Him, and in Him, and they are with Him still. Their hands are His hands, their eyes are His eyes . . . Thus, the icon of a saint, their spiritual portrait, is also an image of Jesus Christ alive in the world. He is the center of each and every icon.