Gregory of Nazianzus

He is called “image” because he is of one substance with the Father; he stems from the Father and not the Father from him, it being the nature of an image to copy the original and to be named after it. But there is more to it than this. The ordinary image is a motionless copy of a moving being. Here we have a living image of a living being, indistinguishable from its original to a higher degree than Seth from Adam and any earthly offspring from its parents. Beings with no complexity to their nature have no points of likeness or unlikeness. They are exact replicas, identical rather than like.

But God will be all in all in the time of restitution; not in the sense that the Father alone will be, and the Son be wholly resolved into him, like a torch into a great pyre, from which it was pulled away for a short time and then put back … when we shall be no longer divided (as we are now by movements and passions) and containing nothing at all of God, or very little, but then we shall be entirely like God, ready to receive into our hearts the whole God and him alone. This is the perfection to which we press on. Paul himself indeed bears witness to this.