Objection 1. It would seem that what belongs to the human nature can be said of the Divine Nature. For what belongs to the human nature is predicated of the Son of God, and of God. But God is His own Nature. Therefore, what belongs to the human nature may be predicated of the Divine Nature.
Objection 2. Further, the flesh pertains to human nature. But as Damascene says (De Fide Orth. iii, 6), "we say, after the blessed Athanasius and Cyril, that the Nature of the Word was incarnate." Therefore it would seem with equal reason that what belongs to the human nature may be said of the Divine Nature.
Objection 3. Further, what belongs to the Divine Nature belongs to Christ's human nature; such as to know future things and to possess saving power. Therefore it would seem with equal reason that what belongs to the human may be said of the Divine Nature.
On the contrary, Damascene says (De Fide Orth. iii, 4): "When we mention the Godhead we do not predicate of it the idioms," i.e. the properties, "of the humanity; for we do not say that the Godhead is passible or creatable." Now the Godhead is the Divine Nature. Therefore what is proper to the human nature cannot be said of the Divine Nature.
I answer that, What belongs to one cannot be said of another, unless they are both the same; thus "risible" can be predicated only of man. Now in the mystery of Incarnation the Divine and human natures are not the same; but the hypostasis of the two natures is the same. And hence what belongs to one nature cannot be predicated of the other if they are taken in the abstract. Now concrete words stand for the hypostasis of the nature; and hence of concrete words we may predicate indifferently what belongs to either nature--whether the word of which they are predicated refers to one nature, as the word "Christ," by which is signified "both the Godhead anointing and the manhood anointed"; or to the Divine Nature alone, as this word "God" or "the Son of God"; or to the manhood alone, as this word "Man" or "Jesus." Hence Pope Leo says (Ep. ad Palaest. cxxiv): "It is of no consequence from what substance we name Christ; because since the unity of person remains inseparably, one and the same is altogether Son of Man by His flesh, and altogether Son of God by the Godhead which He has with the Father."
Reply to Objection 1. In God, Person and Nature are really the same; and by reason of this identity the Divine Nature is predicated of the Son of God. Nevertheless, its mode of predication is different; and hence certain things are said of the Son of God which are not said of the Divine Nature; thus we say that the Son of God is born, yet we do not say that the Divine Nature is born; as was said in I, 39, 5. So, too, in the mystery of Incarnation we say that the Son of God suffered, yet we do not say that the Divine Nature suffered.
Reply to Objection 2. Incarnation implies union with flesh, rather than any property of flesh. Now in Christ each nature is united to the other in person; and by reason of this union the Divine Nature is said to be incarnate and the human nature deified, as stated above (2, 1, ad 3).
Reply to Objection 3. What belongs to the Divine Nature is predicated of the human nature--not, indeed, as it belongs essentially to the Divine Nature, but as it is participated by the human nature. Hence, whatever cannot be participated by the human nature (as to be uncreated and omnipotent), is nowise predicated of the human nature. But the Divine Nature received nothing by participation from the human nature; and hence what belongs to the human nature can nowise be predicated of the Divine Nature.
Source: Summa Theologica (New Advent)