Taken from COMMENTARY ON THE GOSPEL OF ST. JOHN (Aquinas)
Part I: Chapters 1-7 translated by James A. Weisheipl, O.P.
Magi Books, Inc., Albany, N.Y.
Lectio 7: καὶ ὁ λόγος σὰρξ ἐγένετο καὶ ἐσκήνωσεν ἐν ἡμῖν
"But if this were so, it would mean that God did not become man, for one particular suppositum cannot be predicated of another. Accordingly, if the person or suppositum of the Word is different than the person or suppositum of the man, in Christ, then what the Evangelist says is not true, namely, the Word was made flesh. For a thing is made or becomes something in order to be it; if, then, the Word is not man, it could not be said that the Word became man. And so the Evangelist expressly said was made, and not 'assumed,' to show that the union of the Word to flesh is not such as was the 'lifting up' of the prophets, who were not 'taken up' into a unity of person, but for the prophetic act. This union is such as would truly make God man and man God, i.e., that God would be man" (170).
(Sed secundum hoc Deus non esset factus homo; quia impossibile est quod duorum singularium, quae diversa sunt secundum suppositum, unum praedicetur de alio. Unde si alia est persona verbi, seu suppositum, et alia persona hominis, seu suppositum in Christo, tunc non erit verum quod dicit Evangelista verbum caro factum est. Ad hoc enim fit aliquid, ut sit; si ergo verbum non esset homo, non posset dici quod verbum sit factum homo. Et ideo signanter Evangelista dixit factum est, et non dixit assumpsit, ut ostendat quod unio verbi ad carnem non est talis qualis est assumptio prophetarum, qui non assumebantur in unitatem suppositi, sed ad actum propheticum: sed est talis quod Deum vere faceret hominem, et hominem Deum, idest quod Deus esset homo.)
"If you ask how the Word is man, it must be said that he is man in the way that anyone is, man, namely, as having human nature. Not that the Word is human nature itself, but he is a divine suppositum united to a human nature. The statement, the Word was made flesh, does not indicate any change in the Word, but only in the nature newly assumed into the oneness of a divine person. And the Word was made flesh through a union to flesh. Now a union is a relation. And relations newly said of God with respect to creatures do not imply a change on the side of God, but on the side of the creature relating in a new way to God" (172).
(Si vero quaeris quomodo verbum est homo, dicendum quod eo modo est homo quo quicumque alius est homo, scilicet habens humanam naturam. Non quod verbum sit ipsa humana natura, sed est divinum suppositum unitum humanae naturae. Hoc autem quod dicitur verbum caro factum est, non aliquam mutationem in verbo, sed solum in natura assumpta de novo in unitatem personae divinae dicit. Et verbum caro factum est, per unionem ad carnem. Unio autem relatio quaedam est. Relationes autem de novo dictae de Deo in respectu ad creaturas, non important mutationem ex parte Dei, sed ex parte creaturae novo modo se habentis ad Deum.)