As we continue to await the fast-approaching Feast of Holy Christmas, it is good to ponder some aspects of the Incarnation. Among the questions for us to consider is why it was the Son, the Second Person of the Blessed Trinity, that became incarnate, rather than the Father or the Holy Spirit.
Most people have never even thought of this question let alone sought to answer it. God could have chosen many different ways to save us; He chose to act as He did not because it was required, but because it was fitting. It falls to us to ponder, using Scripture and our own reason, why God’s chosen way was fitting, and what we can learn from this.
As always, St. Thomas Aquinas provides rich resources for us. I present below his teaching from the Summa Theologica (part III, question 3, article 8) in bold, italics; my poor commentary appears in red text. St. Thomas proposed four reasons as to why it was most fitting for the Son to become incarnate.
I. First, on the part of the union; for such as are similar are fittingly united. Now the Person of the Son, Who is the Word of God, has a certain common agreement with all creatures, because the word of the craftsman, i.e. his concept, is an exemplar likeness of whatever is made by him. Hence the Word of God, Who is His eternal concept, is the exemplar likeness of all creatures. … for the craftsman by the intelligible form of his art, whereby he fashioned his handiwork, restores it when it has fallen into ruin.
When the Father created all things, he uttered a Word: (i.e., Let there be light). Thus He creates through His Word (the Logos), and the Word of God is Christ. Therefore, in speaking creation into existence by the Logos, God impresses a kind of “logike” (logic) on all things.
In this way the Son, the Logos, has a “certain common agreement with all creatures,” who bear something of logic or likeness to Him. If this be so, then, as St. Thomas reasons, God the Father would best repair His creation by the same Word through whom He first created it.
II. Moreover … Man is perfected in wisdom (which is his proper perfection, as he is rational) by participating the Word of God, as the disciple is instructed by receiving the word of his master. Hence it is said (Sirach 1:5): “The Word of God on high is the fountain of wisdom.” And hence for the consummate perfection of man it was fitting that the very Word of God should be personally united to human nature.
While it is true that Original Sin affected our bodily integrity, perhaps our greatest wound was the darkening of our intellect, which was (and is) our greatest gift, the distinguishing characteristic between us and brute animals. So it is especially fitting that the Word of God, who is also the Wisdom of God, should be joined to our nature and bring healing to us in this way.
St. Paul writes, Do not be conformed to this world, but be transformed by the renewing of your mind. Then you will be able to discern what is the good, pleasing, and perfect will of God (Rom 12:2). Even human words can instruct; all the more, then, can the Word of God made Flesh enlighten and heal us. This shows forth the fittingness that the Word, the Son, the Second Person of the Trinity, should become flesh.
III. The reason of this fitness [of the Second Person becoming flesh] may [also] be taken from the end of the union, which is … the heavenly inheritance, which is bestowed only on sons, according to Romans 8:17: “If sons, heirs also.” Hence it was fitting that by Him Who is the natural Son, men should share this likeness of sonship by adoption, as the Apostle says in the same chapter (Romans 8:29): “For whom He foreknew, He also predestinated to be made conformable to the image of His Son.”
In other words, because it is sons who inherit, it is fitting that He who is Son by nature should become incarnate. And thus shall we, conformed to His image as sons through our adoption and membership in His Body, also inherit the Kingdom and glory through the healing He effects in us.
IV. [Further], the reason for this fitness may be taken from the sin of our first parent, for which Incarnation supplied the remedy. For the first man sinned by seeking knowledge, as is plain from the words of the serpent, promising to man the knowledge of good and evil. Hence it was fitting that by the Word of true knowledge man might be led back to God, having wandered from God through an inordinate thirst for knowledge.
In grasping inordinately for the wrong kind of knowledge (the knowledge of evil) and in insisting on his own right to decide what was good and what was evil, Adam sinned. In and of itself, seeking knowledge is good; it was the object that was disordered (and thus forbidden). Because humans have this thirst to know (of itself good), all the more reason that God should offer us the true Word and Wisdom of God: the Son.
For the Word to become flesh is thus more fitting. In effect, God the Father says, “Let me offer you what you were really seeking, but sought inordinately.” For this reason, the Son, who is the Word, who is Truth itself, becomes incarnate.