Question 5. The parts of human nature which were assumed
Article 1. Whether the Son of God ought to have assumed a true body?
The objections raised here show that there is still doubt that the Son truly became man. An appearance may be acceptable, but a real man is still questioned.
In response, St. Thomas notes that, for the redemption of man, and for all that Christ accomplished through His Passion and Resurrection, only a real and true body would suffice. To truly redeem man, a true man must offer the sacrifice, and this was Jesus the Christ.
“Handle, and see; for a spirit hath not flesh and bones, as you see Me to have.”
Article 2. Whether the Son of God ought to have assumed a carnal or earthly body?
In St. Thomas’ time, it was believed that, most likely, the heavenly bodies such as the stars were of a different substance, something incorruptible, and this must be kept in mind when reading this article.
Again, then, the answer comes down to the real and true humanity of the Son of God. It is not an appearance, not a phantasm, but a real human nature that Christ took. The Word was made flesh. He was not made to appear as flesh, or merely in the “likeness” of flesh, but receiving, from Mary, a real human body, indeed, a real human nature.
Article 3. Whether the Son of God assumed a soul?
This question especially concerns the heresy known as Apollinarianism.
A human nature is constituted of both soul and body. The soul must be a human soul. You would not have a human, say, if a human body were somehow ensouled by an angel, its spirit being the “form of the body.” Likewise, the Divine Person being the soul, the principle of life, in the Body of Christ would mean He took on a human body, but not a human nature. To be a man, you must “be” all that man is, which is the body soul composite. Again, the reality of Christ taking on a human nature, being truly man therefore, is crucial, and all denials of this reality must be refuted to properly understand Christ and the salvation offered in, with, and through Him.
Article 4. Whether the Son of God assumed a human mind or intellect?
Once again, the objections try to replace the human mind, the intellect, with the Divine Person. This is a continuation of the same heresy if properly understood, for the human intellect is the soul. We have an intellectual soul. Without the intellect, you can have a vegetative soul or a sensitive soul, but you will not have a human rational soul, and thus, you do not have a human nature, complete with human soul.
This teaching, likewise, is important for man’s true redemption. Man can understand his purpose as purpose through his mind. This is what makes him rational, and this is also what makes him responsible morally, what gives him the ability to merit or to sin. Without assuming a full human nature, with a human intellect, we say again that “man” would not be redeemed.