Question 4. The mode of union of the part of the human nature
It will be important to keep in mind throughout Aquinas’ understanding of the nature of man as universal, yet only existing in the particular men that actually exist. Many of the platonic or neo-platonic ideas used or implicitly assumed in Christian thought lead to many of the errors and objections which St. Thomas responds to here.
Article 1. Whether human nature was more assumable by the Son of God than any other nature?
Objections: If Christ assumed any nature, to do so would be miraculous, and thus any material nature would be as good as another. However, to become an Angel would be more fitting than to become a material creature.
On the contrary, “My delights were to be with the children of men.”
I answer that, a passive power, such as found in an animal, would not do, but man is made to know and love God, and so it is fitting.
Reply to objections: Of course God could assume any nature, but we are asking what would be proper based on its created nature. This applies to humans and not animals. Man was created in the image and likeness of God, not just in His image.
As per angels, their nature is irredeemable (if fallen), and so there is not fittingness for a saving assumption of an angelic person.
Article 2. Whether the Son of God assumed a person?
Objections: It seems, knowing that human nature always appears in a human person, that the Son of God assumed a human person. This is in accordance with realism, where there is no separate human nature apart from actually existing human persons.
I answer that, The thing assumed is only what is said to be assumed. If it were a person, there would thereby be two persons, for the eternal Person of the Son of God would certainly remain and remain unchanged.
Reply to Objections: There is no assumption of a person by necessity, because the person as “might have been” never was. Instead, the Son of God is the Person in this individual human nature.
Article 3. Whether the Divine Person assumed a man?
Objections: When we say someone became man, we say he became one with a human nature. Thus, they seem interchangeable, and Christ became a man, and a man is a person.
I answer that, What has been assumed (aka as taken for granted), as answered already above, is that the human nature is merely presupposed of the assumption. There was then no particular individual existence of human nature that Christ assumed as if this instance existed before He assumed it.
Reply to Objections: We end up here with a case of equivocation, calling man an instance of human nature and later man as humanity or human nature separately. Properly understood, there is no objection.
Article 4. Whether the Son of God ought to have assumed human nature abstracted from all individuals?
Objection. The Son of God, it seems, should have assumed human nature as such, because salvation is for all men.
I answer that, if the Son of God had assumed human nature as such, then He would have assumed nothing at all, for human nature as such only exists in the mind; in God’s mind as exemplar cause, and in our minds as recognized and extracted from reality.
Perhaps in Platonic thought, dealing with substantial forms as he understood them, this might make sense. But in reality is not so. To have a human nature is to have it in a particular existence. Even if it (human nature) did exist really in this way, it would not be fitting then for a particular person to assume a universal. Likewise, if He had taken on universal human nature, He could not have ascended into Heaven as such.
It seems also to me, human nature, as exemplar cause, is in the Divine Mind from eternity, and to assume this exemplar cause would affect all men, starting with Adam by participation.
Reply to Objection: At the heart of this objection can be seen the false platonic understanding of reality, and human nature therefore, as such.
Article 5. Whether the Son of God ought to have assumed human nature in all individuals?
Here, we have a similar problem to that of article 4. The Son of God, to assume human nature as such, is reflective of an erroneous understanding of reality. Here is where it becomes [even more] important to have a solid grasp of the errors of Plato’s metaphysic, and the correctives of Aristotle’s moderate realism.
It would also not fit either the dignity of men, nor especially of Christ (separate dignities, of course) for Christ to assume human nature as such. All human nature would be the same if it was, as human nature, assumed by Christ. His love for us, moreover, was shown in His, as particular man, suffering for us. Certainly we can unite our suffering to His, carry our cross and follow Him, but this is not our humanity and His as one. He died for us “while we were yet sinners,” an impossibility if He assumed our nature as universal.
Article 6. Whether it was fitting for the Son of God to assume human nature of the stock of Adam?
Objection: It is unfitting for the sinless Son of God to come from the stock of Adam, a sinner. He ought rather assume a human nature from a stock unstained with sin.
In answer, however, it is rather most fitting that God show forth His power by conquering Satan by assuming the very stock of him who was conquered by Satan. Much more, to truly redeem the race of Adam, and therefore truly to redeem man, it is most fitting that He assume the stock of that same man that had fallen, in order to redeem him and all his offspring.
In short, Christ is separated from Adam as regards sin, but not as regards the nature, which includes the flesh. The flesh assumed, yet without sin, is most appropriate as the way to save the flesh from sin. The whole man, and true to man as man, is saved through the Incarnation of Christ, the son of David, the son of Adam.