Leo the Great

But the majesty of the Son of God, in which he is equal with the Father in its garb of a slave’s humility, feared no diminution, required no augmentation. And the very effect of his mercy, which he expended on the restitution of humanity, he was able to bring about solely by the power of his Godhead, thus rescuing the creature that was made in the image of God from the yoke of his cruel oppressor. But because the devil had not shown himself so violent in his attack on the first man as to bring him over to his side without the consent of his free will, the voluntary sin and hostile desires of humanity had to be destroyed in such a way that the standard of justice should not stand in the way of the gift of grace. And therefore in the general ruin of the entire human race there was but one remedy in the secret of the divine plan which could help the fallen, and that was that one of the sons of Adam should be born free and innocent of original transgression, to prevail for the rest both by his example and his merits. Still further, because this was not permitted by natural generation, and because there could be no offspring from our faulty stock without seed, of which the Scripture says, “Who can make a clean thing conceived of an unclean seed? Is it not you who are alone?” David’s Lord was made David’s Son, and sprang from the fruit of the promised branch—One without fault, the twofold nature coming together into one Person, that by one and the same conception and birth might spring our Lord Jesus Christ, in whom was present both true Godhead for the performance of mighty works and true humanity for the endurance of sufferings.