Objection 1. It would seem that this is true: "Man was made God." For it is written (Romans 1:2-3): "Which He had promised before by His prophets in the holy Scriptures, concerning His Son Who was made to Him of the seed of David according to the flesh." Now Christ, as man, is of the seed of David according to the flesh. Therefore man was made the Son of God.
Objection 2. Further, Augustine says (De Trin. i, 13) that "such was this assumption, which made God man, and man God." But by reason of this assumption this is true: "God was made man." Therefore, in like manner, this is true: "Man was made God."
Objection 3. Further, Gregory Nazianzen says (Ep. ad Chelid. ci): "God was humanized and man was deified, or whatever else one may like to call it." Now God is said to be humanized by being made man. Therefore with equal reason man is said to be deified by being made God; and thus it is true that "Man was made God."
Objection 4. Further, when it is said that "God was made man," the subject of the making or uniting is not God, but human nature, which the word "man" signifies. Now that seems to be the subject of the making, to which the making is attributed. Hence "Man was made God" is truer than "God was made man."
On the contrary, Damascene says (De Fide Orth. iii, 2): "We do not say that man was deified, but that God was humanized." Now to be made God is the same as to be deified. Hence this is false: "Man was made God."
I answer that, This proposition, Man was made God, may be understood in three ways. First, so that the participle "made" absolutely determines either the subject or the predicate; and in this sense it is false, since neither the Man of Whom it is predicated was made, nor is God made, as will be said (8,9). And in the same sense this is false: "God was made man." But it is not of this sense that we are now speaking. Secondly, it may be so understood that the word "made" determines the composition, with this meaning: "Man was made God, i.e. it was brought about that Man is God." And in this sense both are true, viz. that "Man was made God" and that "God was made Man." But this is not the proper sense of these phrases; unless, indeed, we are to understand that "man" has not a personal but a simple supposition. For although "this man" was not made God, because this suppositum, viz. the Person of the Son of God, was eternally God, yet man, speaking commonly, was not always God. Thirdly, properly understood, this participle "made" attaches making to man with relation to God, as the term of the making. And in this sense, granted that the Person or hypostasis in Christ are the same as the suppositum of God and Man, as was shown (2, 2,3), this proposition is false, because, when it is said, "Man was made God," "man" has a personal suppositum: because, to be God is not verified of the Man in His human nature, but in His suppositum. Now the suppositum of human nature, of Whom "to be God" is verified, is the same as the hypostasis or Person of the Son of God, Who was always God. Hence it cannot be said that this Man began to be God, or is made God, or that He was made God.
But if there were a different hypostasis of God and man, so that "to be God" was predicated of the man, and, conversely, by reason of a certain conjunction of supposita, or of personal dignity, or of affection or indwelling, as the Nestorians said, then with equal reason might it be said that Man was made God, i.e. joined to God, and that God was made Man, i.e. joined to man.
Reply to Objection 1. In these words of the Apostle the relative "Who" which refers to the Person of the Son of God ought not to be considered as affecting the predicate, as if someone already existing of the "seed of David according to the flesh" was made the Son of God--and it is in this sense that the objection takes it. But it ought to be taken as affecting the subject, with this meaning--that the "Son of God was made to Him ('namely to the honor of the Father,' as a gloss expounds it), being of the seed of David according to the flesh," as if to say "the Son of God having flesh of the seed of David to the honor of God."
Reply to Objection 2. This saying of Augustine is to be taken in the sense that by the assumption that took place in Incarnation it was brought about that Man is God and God is Man; and in this sense both sayings are true as stated above.
The same is to be said in reply to the third, since to be deified is the same as to be made God.
Reply to Objection 4. A term placed in the subject is taken materially, i.e. for the suppositum; placed in the predicate it is taken formally, i.e. for the nature signified. Hence when it is said that "Man was made God," the being made is not attributed to the human nature but to the suppositum of the human nature, Which is God from eternity, and hence it does not befit Him to be made God. But when it is said that "God was made Man," the making is taken to be terminated in the human nature. Hence, properly speaking, this is true: "God was made Man," and this is false: "Man was made God"; even as if Socrates, who was already a man, were made white, and were pointed out, this would be true: "This man was made white today," and this would be false; "This white thing was made man today." Nevertheless, if on the part of the subject there is added some word signifying human nature in the abstract, it might be taken in this way for the subject of the making, e.g. if it were said that "human nature was made the Son of God's."
Source: Summa Theologica (New Advent)