Of the Son of God as Neither Made by the Father Nor Less Than the Father, and of His Incarnation
5 Wherefore The Only-Begotten Son of God was neither made by the Father; for, according to the word of an evangelist, “all things were made by Him:” nor begotten instantaneously; since God, who is eternally wise, has with Himself His eternal Wisdom: nor unequal with the Father, that is to say, in anything less than He; for an apostle also speaks in this wise, “Who, although He was constituted in the form of God, thought it not robbery to be equal with God.” By this catholic faith, therefore, those are excluded, on the one hand, who affirm that the Son is the same [Person] as the Father; for [it is clear that] this Word could not possibly be with God, were it not with God the Father, and [it is just as evident that] He who is alone is equal to no one. And, on the other hand, those are equally excluded who affirm that the Son is a creature, although not such an one as the rest of the creatures are. For however great they declare the creature to be, if it is a creature, it has been fashioned and made. For the terms fashion and create mean one and the same thing; although in the usage of the Latin tongue the phrase create is employed at times instead of what would be the strictly accurate word beget. But the Greek language makes a distinction. For we call that creatura (creature) which they call κτίσμα or κτίσις; and when we desire to speak without ambiguity, we use not the word creare (create), but the word condere (fashion, found). Consequently, if the Son is a creature, however great that may be, He has been made. But we believe in Him by whom all things (omnia) were made, not in Him by whom the rest of things (cetera) were made. For here again we cannot take this term all things in any other sense than as meaning whatsoever things have been made.
6. But as “the Word was made flesh, and dwelt among us,” the same Wisdom which was begotten of God condescended also to be created among men. There is a reference to this in the word, “The Lord created me in the beginning of His ways.” For the beginning of His ways is the Head of the Church, which is Christ endued with human nature (homine indutus), by whom it was purposed that there should be given to us a pattern of living, that is, a sure way by which we might reach God. For by no other path was it possible for us to return but by humility, who fell by pride, according as it was said to our first creation, “Taste, and you shall be as gods.” Of this humility, therefore, that is to say, of the way by which it was needful for us to return, our Restorer Himself has deemed it meet to exhibit an example in His own person, “who thought it not robbery to be equal with God, but emptied Himself, taking the form of a servant;” in order that He might be created Man in the beginning of His ways, the Word by whom all things were made. Wherefore, in so far as He is the Only-begotten, He has no brethren; but in so far as He is the First-begotten, He has deemed it worthy of Him to give the name of brethren to all those who, subsequently to and by means of His pre-eminence, are born again into the grace of God through the adoption of sons, according to the truth commended to us by apostolic teaching. Thus, then, the Son according to nature (naturalis filius) was born of the very substance of the Father, the only one so born, subsisting as that which the Father is, God of God, Light of Light. We, on the other hand, are not the light by nature, but are enlightened by that Light, so that we may be able to shine in wisdom. For, as one says, “that was the true Light, which lights every man that comes into the world.” Therefore we add to the faith of things eternal likewise the temporal dispensation of our Lord, which He deemed it worthy of Him to bear for us and to minister in behalf of our salvation. For in so far as He is the only-begotten Son of God, it cannot be said of Him that He was and that He shall be, but only that He is; because, on the one hand, that which was, now is not; and, on the other, that which shall be, as yet is not. He, then, is unchangeable, independent of the condition of times and variation. And it is my opinion that this is the very consideration to which was due the circumstance that He introduced to the apprehension of His servant Moses the kind of name [which He then adopted]. For when he asked of Him by whom he should say that he was sent, in the event of the people to whom he was being sent despising him, he received his answer when He spoke in this wise: “I Am that I Am.” Thereafter, too, He added this: “Thus shall you say unto the children of Israel, He that is (Qui est) has sent me unto you.”
7. From this, I trust, it is now made patent to spiritual minds that there cannot possibly exist any nature contrary to God. For if He is—and this is a word which can be spoken with propriety only of God (for that which truly is remains unchangeably; inasmuch as that which is changed has been something which now it is not, and shall be something which as yet it is not)—it follows that God has nothing contrary to Himself. For if the question were put to us, What is contrary to white? We would reply, black; if the question were, What is contrary to hot? We would reply, cold; if the question were, What is contrary to quick? We would reply, slow; and all similar interrogations we would answer in like manner. When, however, it is asked, What is contrary to that which is? The right reply to give is, that which is not.
8. But whereas, in a temporal dispensation, as I have said, with a view to our salvation and restoration, and with the goodness of God acting therein, our changeable nature has been assumed by that unchangeable Wisdom of God, we add the faith in temporal things which have been done with salutary effect on our behalf, believing in that Son of God Who Was Born Through the Holy Ghost of the Virgin Mary. For by the gift of God, that is, by the Holy Spirit, there was granted to us so great humility on the part of so great a God, that He deemed it worthy of Him to assume the entire nature of man (totum hominem) in the womb of the Virgin, inhabiting the material body so that it sustained no detriment (integrum), and leaving it without detriment. This temporal dispensation is in many ways craftily assailed by the heretics. But if any one shall have grasped the catholic faith, so as to believe that the entire nature of man was assumed by the Word of God, that is to say, body, soul, and spirit, he has sufficient defense against those parties. For surely, since that assumption was effected in behalf of our salvation, one must be on his guard lest, as he believes that there is something belonging to our nature which sustains no relation to that assumption, this something may fail also to sustain any relation to the salvation. And seeing that, with the exception of the form of the members, which has been imparted to the varieties of living objects with differences adapted to their different kinds, man is in nothing separated from the cattle but in [the possession of] a rational spirit (rationali spiritu), which is also named mind (mens), how is that faith sound, according to which the belief is maintained, that the Wisdom of God assumed that part of us which we hold in common with the cattle, while He did not assume that which is brightly illumined by the light of wisdom, and which is man's peculiar gift?
Source: On Faith and the Creed (New Advent)