Thomas Aquinas - Summa Theologica, Part III (Tertia Pars)

On the contrary, Whatever the Father can do, that also can the Son do. But after the Incarnation the Father can still assume a human nature distinct from that which the Son has assumed; for in nothing is the power of the Father or the Son lessened by the Incarnation of the Son. Therefore it seems that after the Incarnation the Son can assume another human nature distinct from the one He has assumed.

I answer that, What has power for one thing, and no more, has a power limited to one. Now the power of a Divine Person is infinite, nor can it be limited by any created thing. Hence it may not be said that a Divine Person so assumed one human nature as to be unable to assume another. For it would seem to follow from this that the Personality of the Divine Nature was so comprehended by one human nature as to be unable to assume another to its Personality; and this is impossible, for the Uncreated cannot be comprehended by any creature. Hence it is plain that, whether we consider the Divine Person in regard to His power, which is the principle of the union, or in regard to His Personality, which is the term of the union, it has to be said that the Divine Person, over and beyond the human nature which He has assumed, can assume another distinct human nature.

Reply Obj. 1: A created nature is completed in its essentials by its form, which is multiplied according to the division of matter. And hence, if the composition of matter and form constitutes a new suppositum, the consequence is that the nature is multiplied by the multiplication of supposita. But in the mystery of the Incarnation the union of form and matter, i.e. of soul and body, does not constitute a new suppositum, as was said above (A. 6). Hence there can be a numerical multitude on the part of the nature, on account of the division of matter, without distinction of supposita.

Reply Obj. 2: It might seem possible to reply that in such a hypothesis it would follow that there were two men by reason of the two natures, just as, on the contrary, the three Persons would be called one man, on account of the one nature assumed, as was said above (A. 6, ad 1). But this does not seem to be true; because we must use words according to the purpose of their signification, which is in relation to our surroundings. Consequently, in order to judge of a word's signification or co-signification, we must consider the things which are around us, in which a word derived from some form is never used in the plural unless there are several supposita. For a man who has on two garments is not said to be "two persons clothed," but "one clothed with two garments"; and whoever has two qualities is designated in the singular as "such by reason of the two qualities." Now the assumed nature is, as it were, a garment, although this similitude does not fit at all points, as has been said above (Q. 2, A. 6, ad 1). And hence, if the Divine Person were to assume two human natures, He would be called, on account of the unity of suppositum, one man having two human natures. Now many men are said to be one people, inasmuch as they have some one thing in common, and not on account of the unity of suppositum. So likewise, if two Divine Persons were to assume one singular human nature, they would be said to be one man, as stated (A. 6, ad 1), not from the unity of suppositum, but because they have some one thing in common.

Reply Obj. 3: The Divine and human natures do not bear the same relation to the one Divine Person, but the Divine Nature is related first of all thereto, inasmuch as It is one with It from eternity; and afterwards the human nature is related to the Divine Person, inasmuch as it is assumed by the Divine Person in time, not indeed that the nature is the Person, but that the Person of God subsists in human nature. For the Son of God is His Godhead, but is not His manhood. And hence, in order that the human nature may be assumed by the Divine Person, the Divine Nature must be united by a personal union with the whole nature assumed, i.e. in all its parts. Now in the two natures assumed there would be a uniform relation to the Divine Person, nor would one assume the other. Hence it would not be necessary for one of them to be altogether united to the other, i.e. all the parts of one with all the parts of the other. _______________________

EIGHTH ARTICLE [III, Q. 3, Art. 8]

Whether it was more fitting that the Person of the Son rather than any other Divine Person should assume human nature?

Objection 1: It would seem that it was not more fitting that the Son of God should become incarnate than the Father or the Holy Ghost. For by the mystery of the Incarnation men are led to the true knowledge of God, according to John 18:37: "For this was I born, and for this came I into the world, to give testimony to the truth." But by the Person of the Son of God becoming incarnate many have been kept back from the true knowledge of God, since they referred to the very Person of the Son what was said of the Son in His human nature, as Arius, who held an inequality of Persons, according to what is said (John 14:28): "The Father is greater than I." Now this error would not have arisen if the Person of the Father had become incarnate, for no one would have taken the Father to be less than the Son. Hence it seems fitting that the Person of the Father, rather than the Person of the Son, should have become incarnate.

Obj. 2: Further, the effect of the Incarnation would seem to be, as it were, a second creation of human nature, according to Gal. 6:15: "For in Christ Jesus neither circumcision availeth anything, nor uncircumcision, but a new creature." But the power of creation is appropriated to the Father. Therefore it would have been more becoming to the Father than to the Son to become incarnate.

Obj. 3: Further, the Incarnation is ordained to the remission of sins, according to Matt. 1:21: "Thou shalt call His name Jesus. For He shall save His people from their sins." Now the remission of sins is attributed to the Holy Ghost according to John 20:22, 23: "Receive ye the Holy Ghost. Whose sins you shall forgive, they are forgiven them." Therefore it became the Person of the Holy Ghost rather than the Person of the Son to become incarnate.

On the contrary, Damascene says (De Fide Orth. iii, 1): "In the mystery of the Incarnation the wisdom and power of God are made known: the wisdom, for He found a most suitable discharge for a most heavy debt; the power, for He made the conquered conquer." But power and wisdom are appropriated to the Son, according to 1 Cor. 1:24: "Christ, the power of God and the wisdom of God." Therefore it was fitting that the Person of the Son should become incarnate.

I answer that, It was most fitting that the Person of the Son should become incarnate. 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. And therefore as creatures are established in their proper species, though movably, by the participation of this likeness, so by the non-participated and personal union of the Word with a creature, it was fitting that the creature should be restored in order to its eternal and unchangeable perfection; for the craftsman by the intelligible form of his art, whereby he fashioned his handiwork, restores it when it has fallen into ruin. Moreover, He has a particular agreement with human nature, since the Word is a concept of the eternal Wisdom, from Whom all man's wisdom is derived. And hence 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 (Ecclus. 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.