Tertullian, Against Marcion 2.27

Now then, to finish the rest by a short cut: whatever you still gather as tiny and weak and unworthy for the Creator’s destruction, I will set out by a simple and sure reason — that God could not enter human dealings unless he had taken up human senses and affections too, through which he might temper by humility the force of his majesty, intolerable of course to human mediocrity. Unworthy of himself, yes, but necessary for man, and so already worthy of God, because nothing is so worthy of God as man’s salvation.

I would reopen this at more length if I were dealing with pagans — though with heretics the meeting is not much different — but since you yourselves have already believed that God stayed in a figure and in the rest of the order of the human condition, you will not demand to be persuaded longer that God conformed himself to humanity; you are refuted from your own faith. For if God, and a higher one at that, laid low the peak of his majesty with such humility that he was even subjected to death, and a cross’s death, why do you not think some smallnesses also fitted our God — yet more bearable than Jewish insults and gibbets and tombs? Or are these the smallnesses that ought already from here to prejudge that Christ, exposed to human passions, belongs to that God whose humanities you cast in his teeth? For we also confess that Christ always acted in the Father God’s name — himself conversing from the beginning, himself meeting with patriarchs and prophets, the Creator’s Son, his Word, whom by bringing forth from himself he made Son and from then set over every arrangement and will of his, lessening him a little under the angels, as it is written with him. By that lessening he was also arranged by the Father for these things you blame as human, learning already from the beginning what he was going to be at the end.

He is the one who comes down, who asks, who requests, who swears. But because the Father has been seen by no one, the shared gospel will also witness, with Christ saying: No one has known the Father except the Son. For he himself had also declared in the old testament: No one will see God and live — determining the invisible Father, in whose authority and name he himself was God who was seen, the Son of God. But with us too Christ is taken in the person of Christ, because in this way also he is ours. Therefore whatever you demand as worthy of God will be held in the invisible, unapproachable, calm Father — and, so to speak, the philosophers’ God — but whatever you blame as unworthy will be counted to the Son, seen and heard and met, the Father’s umpire and minister, mixing in himself man and God: God in powers, man in smallnesses, so that he may confer on man as much as he takes from God. In short, the whole disgrace of my God among you is the sacrament of human salvation. God was conversing in a human way so that man might be taught to act in a divine way. God was acting on equal terms with man so that man might be able to act on equal terms with God. God was found little so that man might become great.