A few days ago, I got involved in a thread started by Dr. Edgar Foster—at his blog Foster's Theological Reflections—under the title: Question of the Day for Trinitarians.
Among other issues, Dr. Foster and I discussed Aquinas's understanding of Jesus statement that, "the Father is greater than I" (John 14:28). I stated, that Aquinas believed that it could be understood to apply to both of Jesus' natures (i.e. divine and human); Edgar (who is quite knowledgeable and no novice when it comes to Aquinas), is of the opinion that Aquinas limited the interpretation to his human nature only. I quoted in our combox discussion the same selection from Aquinas's commentary on the Gospel of John that I provided in my April 1, 2016 thread, Clear elements of Nicene Monarchism..., which I believe supports my take. Here is that selection again:
1971 One could also say, as Hilary does, that even according to the divine nature the Father is greater than the Son, yet the Son is not inferior to the Father, but equal. For the Father is not greater than the Son in power, eternity and greatness, but by the dignity of a grantor or source. For the Father receives nothing from another, but the Son, if I can put it this way, receives his nature from the Father by an eternal generation. So, the Father is greater because he gives; but the Son is not inferior, but equal, because he receives all that the Father has: "God has bestowed on him the name which is above every name" (Phil 2:9). For the one to whom a single act of existence (esse) is given, is not inferior to the giver. [LINK to online source.]
The above did not convince Edgar of my position, so to add strength to my view, I am providing yet another selection from Aquinas's commentary on the Gospel of John, this time from John 5:19:
746 To get the true meaning of Christ’s statement, we should know that in those matters which seem to imply inferiority in the Son, it could be said, as some do, that they apply to Christ according to the nature he assumed; as when he said: “The Father is greater than I” (below 14:28). According to this, they would say that our Lord’s statement, the Son cannot do anything of himself, should be understood of the Son in his assumed nature. However, this does not stand up, because then one would be forced to say that whatever the Son of God did in his assumed nature, the Father had done before him. For example, that the Father had walked upon the water as Christ did: otherwise, he would not have said, but only what he sees the Father doing.
And if we say that whatever Christ did in his flesh, God the Father also did in so far as the Father works in him, as said below (14:10): “The Father, who lives in me, he accomplishes the works,” then Christ would be saying that the Son cannot do anything of himself, but only what he sees the Father doing in him, i.e., in the Son. But this cannot stand either, because Christ’s next statement, For whatever the Father, does, the Son does likewise, could not, in this interpretation, be applied to him, i.e., to Christ. For the Son, in his assumed nature, never created the world, as the Father did. Consequently, what we read here must not be understood as pertaining to Christ’s assumed nature.
747 According to Augustine, however, there is another way of understanding statements which seem to, but do not, imply inferriority in the Son: namely, by referring them to the origin of the Son coming or begotten from the Father. For although the Son is equal to the Father in all things, he receives all these things from the Father in an eternal begetting. But the Father gets these from no one, for he is unbegotten. According to this explanation, the continuity of thought is the following: Why are you offended because I said that God is my Father, and because I made myself equal to the Father? Amen, amen, I say to you, the Son can do nothing of himself. As if to say: I am equal to the Father, but in such a way as to be from him, and not he from me; and whatever I may do, is in me from the Father.
748 According to this interpretation, mention is made of the power of the Son when he says, can, and of his activity when he says, do. Both can be understood here, so that, first of all, the derivation of the Son’s power from the Father is shown, and secondly, the conformity of the Son’s activity to that of the Father.
749 As to the first, Hilary explains it this way: Shortly above our Lord said that he is equal to the Father. Some heretics, basing themselves on certain scriptural texts which assert the unity and equality of the Son to the Father, claim that the Son is unbegotten. For example, the Sabellians, who say that the Son is identical in person with the Father. Therefore, so you do not understand this teaching in this way, he says, the Son cannot do anything of himself, for the Son’s power is identical with his nature. Therefore the Son has his power from the same source as he has his being (esse); but he has his being (esse) from the Father: “I came forth from the Father, and I have come into the world” (Jn 16:28). He also has his nature from the Father, because he is God from God; therefore, it is from him that the Son has his power (posse).
So his statement, the Son cannot do anything of himself, but only what he sees the Father doing, is the same as saying: The Son, just as he does not have his being (esse) except from the Father, so he cannot do anything except from the Father. For in natural things, a thing receives its power to act from the very thing from which it receives its being: for example, fire receives its power to ascend from the very thing from which it receives its form and being. Further, in saying, the Son cannot do anything of himself, no inequality is implied, because this refers to a relation; while equality and inequality refer to quantity. (Bold emphasis in the original.) [LINK]
In my opinion, I think the above comments make it quite clear that Aquinas applies John 14:28 and John 5:19 to both of Jesus' natures. Would be very interested in hearing from others on this issue...
Grace and peace,