This is my first summary of St. Thomas Aquinas for my Christology class. Feel free to offer corrections. Some of the objections and responses are less than clear to me.
In Article 1, St. Thomas deals with whether it was fitting that God become incarnate. Addressing first the objection, he responds that immutable God is not changed in state from this unity, but that the mutable creature is changed. While man is not naturally endowed with this dignity (Obj. 2), God’s goodness made this unity fitting for our salvation. St. Thomas notes the confusion with which objection 3 treats the matter of evil, returning to the distinction he makes in PI, Q48, A5 between evil of pain and evil of fault. Finally, he underscores that God is not great in material terms but in terms of might or power (potentia). He notes that the end of the material world is itself to make known “the invisible things of God” and that it is most fitting for God, who is goodness itself, to communicate that goodness to man, whose nature is reasonable, in a means that befits the highest manner of the creature (which would be reason or logos).
In Article 2. St. Thomas first responds is to the definition of “necessary,” that the Incarnation was not exclusively necessary but suitably necessary in that it accomplished what needed to be done and did so for the “furtherance of our good”—that is, as Augustine noted in De Trinitate xiii, it demonstrated God’s love for us by condescending to share our lot. Through the Incarnation, He instills in us faith and hope, and through His demonstration of love, gains our love in return. In addition, He gives us an example to be followed and, by uniting Himself to flesh, divinizes humanity, as the Early Fathers would say. In addition to this “furtherance of good” is a withdrawal from evil, in which, being united to God, we understand our true dignity, not as some merit of ours but as a gift from God.
St. Thomas acknowledges in Article 3 a diversity of opinion on the question of whether God would have become incarnate had man not sinned, he comes down on the side of those who say He would not have become incarnate. He notes in response to objection 1 that all causes assigned in article 2 (the previous article) pertained to remedies for sin, and in response to objection 2 that all that is required for the perfection of nature is that creatures be ordered toward God as their natural ends. While St. Thomas agrees that God certainly could have become incarnate in any case, none of the objections necessitate that God become incarnate in such case. However, scripture makes clear that the purpose of the Incarnation was the redemption of man from sin, as the author notes in Luke 19:10 and Ephesians 5:32.
As sin came into the world through one man, one man would defeat sin through His action. St. Thomas notes in Article 4 that the Lamb comes to absolve the sins of the world. While this undoubtedly includes actual sins, it must primarily address the first cause of sin, the original fall. As Paul notes in Romans, many died through one man’s sin, but many more have “the free gift in the grace of that one man Jesus Christ abounded for many” (5:15, RSV). One of the distinctions the Angelic Doctor makes in this article is between intensive and extensive greatness of sin, the former which is hereditary and the latter, voluntary (II, 81, 1). While actual sin may be more grievous in a personal sense, its effects are limited in scope to the individual, while the effects of original are more extensive, applying to all humanity.
In Article 5, St. Thomas addresses objections that charity, effectiveness, and perfection of grace would all have been better served had God become incarnate at the beginning of the human race. He counters that God in His Divine wisdom knew best when and where the Incarnation was needed and would be most effective for the perfection of human nature. Because the Incarnation was provided as a remedy for sin, it was only fitting for the Incarnation to come after the fall. He also points out the root of Adam’s fall in pride and the need to bring us to humility to recognize our need for grace. Come too soon, and man would fail to recognize his need for a liberator. The furtherance of our good required the spiritual man to follow the “earthy” man (adamah). In addition, Christ’s dignity necessitated that He be preceded by heralds who went before Him. Finally, so that the fervor of those coming to faith did not grow cold toward the end of time, it was fitting that God become Incarnate when he did, and not at the beginning of the human race.
In Article 6, St. Thomas points out that the Incarnation is both perfect Himself and also our means of perfection. In this sense perfection both precedes our imperfection, but in terms of our nature, follows imperfection. By coming when He did, He found us in our imperfection, when we most needed His grace and when we would be most likely to respond. Had he come at the end, memory and reverence of Him may have been forgotten, along with the natural law and morality. By coming neither at the beginning of the human nor at the end of the world, God saves through faith in past, present, and future events.