Benedict XVI has a great respect for St. Maximus the Confessor as the protagonist of Constantinople III (680-681), the Council that resolved the dualism of the two natures in Christ that were understood to be “in parallel” and the key to the widely unresolved dualisms that continue to obtain in the present day: grace/nature; faith/reason, Church/ State, etc. Benedict refers to the reshaping of the question from a relationship of natures to the deployment of two wills by the one Subject, the Logos of the Father. It seems that the question migrated from the human nature of Christ as an agency operating immanently within the created cosmos, to the Agency of the divine Subject who wills immanently within the created cosmos. In a word, Chalcedon was not the last word since it left the Christological account in a state of “parallel” (seemingly autonomous) natures where – to this day – the sufferings of Christ is disputed as to whether Christ suffered as God or as man. The operative concept is “immutability.” In dealing with natures as objects, to suffer involves change in being. To suffer, one must lose ontological density. If God is supreme, unchanging Being, then He cannot change or lose ontological density and still be God. Hence, He cannot suffer as God. And since Chalcedon defined that, indeed, Christ is true and complete man by possession of a human nature, then His suffering must be accounted for in and by the human nature. This is the parallelism of the two natures as principles of two ontological levels of activity, the divine and the human. Suffering, then, is human. Or, we could say it is divine because it takes place in a divine Person, but the actual suffering would have to be of, in and by the human nature itself because the immutability of the divine Person would impede it.
But what if we went deeper and ascertained that only subjects are the free and responsible agents of moral, human action. Natures don’t act; they operate. And if we take St. Thomas’s assessment of the number of existential principles in Jesus Christ, we find that there are not two acts of existence, but one, the Esse personale of the Son. The entire Being of Christ is dynamized in being and act by the personal act of existence of the divine Son. And this without prejudice to the ontological integrity of the human nature and the freedom of the human will. Nay, the human will, made in the image and likeness of the divine, is enhanced as self-gift. The free and responsible Agent of all being and action in Jesus Christ is the Son, and the human willing is an operation, not of a nature but of the Son Himself. Hence, all the suffering that occurs in Christ because of the humanity, is the suffering of the divine Person – the Eternal Absolute - Who is the Subject-Agent of all Being and acting in Christ.
In a word, Constantinople III completes the development of truth of Chalcedon, and the protagonist of that work and completion has been Maximus.
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Benedict XVI writes on June 25, 2008: "He Always Had As His Compass the Concrete Reality of the World"
“Maximus did not accept any attempt to minimize the humanity of Christ. The theory had arisen according to which Christ had only one will, the divine. To defend the uniqueness of his person, they denied he had a true human will.”At first glance, it might appear to be something good that in Christ there was only one will. “However, St. Maximus understood immediately that this would have destroyed the mystery of salvation, because a humanity without will -- a man without a will -- is not a true man, but rather an amputated man. Therefore, the man Jesus Christ would not have been a true man, would not have experienced the drama of the human being, which consists precisely in the difficulty of conforming our will with the truth of being.
”Thus St. Maximus affirmed with great determination: Sacred Scripture does not show us an amputated man, without a will, but a true complete man: God, in Jesus Christ, has truly assumed the totality of the human being -- obviously except for sin -- hence, also, a human will. Stated that way, the question was clear: Christ is either a true man or not. ”However, the problem arises: Does not one end in this way in a sort of dualism? Is not one faced with affirming two complete personalities with reason, will, sentiment? How can this dualism be overcome? How can the completeness of the human being be preserved while protecting the unity of the person of Christ, who was not schizophrenic?”St. Maximus demonstrates that man finds his unity, the integration of himself, his totality not in himself, but in surpassing himself, by coming out of himself. Thus, also in Christ, man, coming out of himself, finds in God, in the Son of God, himself.”Man must not "amputate" the human Christ to explain the Incarnation. One must only understand the dynamism of the human being who is fulfilled only by coming out of himself. Only in God do we find ourselves, our totality and our completeness.”Thus we see that it is not the man who is closed in on himself who is complete the man, but it is the man who opens himself, who comes out of himself -- it is he who becomes complete, who finds himself in the Son of God, he finds in him his true humanity.”For St. Maximus this vision does not remain a philosophical speculation. He sees it realized in the concrete life of Jesus, above all in the drama of Gethsemane.”In this drama of Jesus' agony, of anguish and death, of the opposition between the human will not to die and the divine will that offers itself to death, in this drama of Gethsemane the whole human drama is realized, the drama of our redemption. St. Maximus tells us, and we know that this is true: Adam -- and Adam is us -- thought that the "no" was the apex of liberty; that only he who can say "no" is truly free; that to truly realize his liberty, man must say "no" to God.
”Only in this way, he thinks, he is finally himself; he has arrived at the summit of liberty. This tendency was also present in Christ's human nature, but he overcame it, because Jesus saw that "no" is not the greatest liberty. The greatest liberty is to say "yes," to conform with the will of God. Only in saying "yes" does man really become himself. Only in the great opening of the "yes," in the unification of his will with the divine will, does man become immensely open, he becomes "divine."”To be like God was Adam's desire, namely, to be completely free. However, he is not divine, the man who is closed in on himself is not completely free. He is so by coming out of himself, it is in the "yes" that he becomes free. And this is the drama of Gethsemane: not my will but yours.”Transferring one's will to the divine will, that is how a true man is born. That is how we are redeemed. ”This, in a few words, is the fundamental point of what St. Maximus wished to say, and we see that here the whole human being is questioned; here is the whole question of our life.”St. Maximus already had problems in Africa defending this vision of man and of God; then he was called to Rome. In 649 he took an active part in the Lateran Council, called by Pope Martin I to defend the two wills of Christ, against the emperor's edict, which -- pro bono pacis -- prohibited the discussion of this question.”Pope Martin paid dearly for his courage: Although he was in poor health, he was arrested and taken to Constantinople. Prosecuted and condemned to death, his sentence was commuted to final exile in Crimea, where he died on Sept. 16, 655, after two long years of humiliation and torments.”
 S. Th. III, 17, 2, ad 2.