Aquinas is clearly in step with the tradition that can be traced from Nicea, through Augustine and the Lombard, to the heart of the Middle Ages. One thing to briefly note is that even in his densest argumentation, Aquinas was not trying to prove elements of his theology via rational argument as that is impossible and not fitting given the topic. Things like the incarnation are held by faith with reason to help one understand better. We will cover three main topics, pre-existence, the two natures, and the mission of the Son and his relation to the other members of the Trinity before we move into a brief discussion of Jesus as king.
One can get a sense for how settled the topic of the pre-existence of the Son was by Aquinas day by how brief and straight-forward his presentation was. The Son pre-existed as a divine person in eternity past. Only his human nature was created. On the other hand, the humanity of the Son and the union between the human and divine receives extended discussion.
Aquinas devotes the first nineteen questions in Tertia Pars to the incarnation and to understanding how the two natures co-exist. For Aquinas it was important that the natures were indeed two. In the incarnation we did not have two natures joining together to make something new. Neither however do we have two persons. The single person of the incarnate Son possessed two united natures. They are so united, that “words which are said of Christ either in his divine or his human nature may be said of either God or man.” He also extensively delves into questions surrounding the divine attributes that Jesus possessed and what his limitations were. One that clearly was a big deal was the extent of Jesus’ knowledge. Aquinas was clearly concerned to affirm the full humanity of Jesus while not undermining his divinity. Humanity required potentiality when it came to knowledge. What is interesting, however, is how Aquinas believed Jesus learned. It was only via discovery, because it would be improper for him, also being divine, to be taught anything. In his divine nature, Jesus possessed complete knowledge as is necessary given his role as the judge of man.
So how did Aquinas understand the mission of the Son and the relation between Father and Son? The relation is what makes the person of the Godhead. What makes the Son, the Son, in distinction from the Father, is the way he relates to the Father. Aquinas cites Augustine when discussing the issue of subordination, saying that the Son is only subordinate “in the form of a servant” because, in his human nature, he did not attain to the goodness of the Father. Human nature is inherently inferior to divine nature. Jesus’ prayer of agony in the garden in Mt. 26:39 can be understood along these lines. It was a demonstration of the submission of a sensual human will to the will of God.
The Son is sent by the Father, and this in no way implies subordination, but is linked to his mission. The Son was not sent to a place where he was not before, since God is everywhere, but is best understood as consisting in “… a new mode of presence in the person sent, his rendering himself in an innovative way.” In other words, he was sent into a new mode of being or revelation, not a new location. The Father, especially his wisdom, was revealed in the incarnation. For this reason the Son came as a human, a rational creature. The Father sends the Son and works through him as one united cause.
Eschatology makes up the conclusion of Aquinas’ work on Christology. Jesus will return as the divine judge and he is sitting at the right hand of the Father, possessing judicial power. The Son is co-regent with the Father. For Aquinas, 1 Cor. 8:6 is programmatic and he interprets the verse as describing their unity of governance. This is an ongoing governance of all of creation. His rule is very much in the here and now and will be displayed dramatically upon his return.
As we can see there has been both consistency and variation among the greatest theologians of the church up to the time of the Reformation. No one would object to our statement that Jesus is the divine king, though some would emphasize that more than others. For some it’s an afterthought outside of eschatology, while others emphasize the importance of Jesus rule now.
His divinity garnered a lot more discussion. Clearly the Father acts through the Son and there is a complete unity of wills between them. Many of the earliest theologians found hierarchy in this relationship with the Son being subordinate to the Father. Over time the church refined its understanding of their relationship and any distinction between Father and Son was understood as reducible to the way they relate to each other. As the focus on the Son’s divinity increased through the centuries, we also see more discussion on what it meant for him to be human. All tried to preserve his humanity, some succeeded better than others. Also, was his humanity divinized, were his natures mixed into something new, or were his two natures in contact but always distinct? Here no consensus formed among the theologians we consulted, though over time divinization clearly fell out of favor.
 I will abbreviate Summa Theologiae as ST and all quotations from the Summa are from Shapcote’s translation. Wawrykow 2005 p. 233.
 Wawrykow 2005 p. 228 and also Emery 2007 pp.25-26. I appreciate that I never sensed any of the hand waving of Augustine anywhere in the portions of ST that I read.
 My treatment of Aquinas is very selective, otherwise it could easily turn into a paper of its own.
 ST.TP.Q2.A6, c.f., ST.TP.Q17. Aquinas pushes back hard against a Christology of mixture. Aquinas also makes clear that the union is not eternal (presumably he believes it begins in the incarnation) in ST.TP.Q2.A7. Also see the strong affirmation of ST.TP.Q16.A1 that in Jesus, ‘God is man,’ i.e., Jesus was a member of the Trinity. Wawrykow 2005 has a nice discussion on pp. 225-27. It is also important to note that Aquinas pushes back against the notion of a divinized human nature. Christ as man is not God. See ST.TP.Q16.A3, A7, A11.
 ST.TP.Q16.A4 with due qualifications.
 See esp. Gondreau 2005 passim, esp. p. 255.
 I.e., he gained empirical knowledge.
 ST.TP.Q9.A4. Davies 2014 p. 303, c.f., Gondreau 2005 p. 267. This is a place where I think his balancing act falls apart. I see no reason why Jesus couldn’t be taught. However, I appreciate the point Gondreau makes, that even going this far was groundbreaking.
 ST.TP.Q10.A2. Davies 2014 p. 302. Other discussion points include omnipotence (he didn’t have it) and Christ’s “defects.” Sinfulness was obviously not one of them. Jesus did not even have the capacity to sin. Pain and fear were (though the discussion on his fear is pretty complex). See ST.TP.Q13-Q15.
 More precisely, “…the person cannot be known independently of the relative property which constitutes it as such.” Emery 2007 p. 120.
 The word distinction is intentionally chosen here. For Aquinas, there are no differences between persons in the Trinity, only distinctions. See Emery 2007, pp. 134-35. This move by Aquinas, though not completely innovative on his part, provides the most satisfactory classical explanation of the Trinity of anyone I have read to date. See Emery 2007, pp. 87-96 for a full presentation.
 Emery 2007 p. 367, emphasis original.
 On the importance of revelation to the divine mission see Emery 2007, pp. 200-04.
 Emery explains that this was also the way to redeem all of creation, as Aquinas understood humanity as summing up all of the created order. This is an interesting suggestion if humans are indeed the end of the evolutionary processes that God used to bring life to this earth. His coming as a creature was necessary for mediation to take place at all, see ST.TP.Q26,A2.
 Emery 2005, p. 71. C.f., Wittman 2016, p. 154.
 ST.PP.Q58-Q59. Davies 2014, p. 322. It is important to Aquinas to affirm that the Son will return while possessing both a divine and human nature.