We may and must say in all truth, "God is man," for one and the same Person who is God is man also; "Man is God," for a Person who is truly man is a Person who is God; all that is proper to and belongs to human nature can be said of God, for all such belongs to a Person who is God, and all that is proper to the divine nature can be said of man who is the Son of God, for this man is a Person who is God. But we may not say of the divinity what is said of the humanity, or conversely, because these two natures remain distinct and each has its own properties (XVI. 1,2).
May one say "God was made man"?
Yes, because the Person who is God began to be truly man at a particular time before which It was not man (XVI. 6).
May one also say "Man was made God"?
No, for this presupposes that there was a person who was a man first of all without being God, and that afterwards he became God (XVI. 7).
May one say "Christ is a creature"?
One may not say this altogether; but it may be said provided one adds, "by reason of the human nature which is united hypostatically to Him," for it is true that this human nature is something created (XVI. 8).
May one say "This man," meaning Jesus Christ, "began to exist"?
No, for the sense would be that the Person of God the Son began to exist. But it may be said provided one adds, "in so far as He is man," or "by reason of His human nature " (XVI. 9).
Next - The Catechism of the Summa - Tertia Pars - XI. OF THE UNITY AND MULTIPLICITY IN JESUS CHRIST: AS REGARDS HIS BEING; AS REGARDS HIS WILL; AND AS REGARDS HIS OPERATIONS (A)