Chapter 9.
109 Again, their aimless and futile question finds no loophole for entry, even when directed upon the creation itself; nay, indeed, temporal existences appear, in certain cases, to admit of no division of time. For instance, light generates radiance, but we can neither conceive that the radiance begins to exist after the light, nor that the light is in existence before the radiance, for where there is a light, there is radiance, and where there is radiance there is also a light; and thus we can neither have a light without radiance, nor radiance without light, because both the light is in the radiance, and the radiance in the light. Thus the Apostle was taught to call the Son “the Radiance of the Father's Glory,” for the Son is the Radiance of His Father's light, co-eternal, because of eternity of Power; inseparable, by unity of brightness.
110. If then we can neither understand the mystery of, nor dissociate, these created objects in the sky above us, which we see, can we comprehend Him Whom we see not, Who is above every created existence, God, as He is in the very Holy of Holies of His own Generation? Can we make time a barrier between Him and the Son, when all time is the creation of the Son?
111. Let them cease therefore, and say no more that before He was begotten the Son was not. For the word “before” is a mark of time, whereas the Generation is before all times, and therefore that which comes after anything comes not before it, and the work cannot be before the maker, seeing that necessarily objects made take their commencement from the craftsman who makes them. How can the customary action of any created object be regarded as existing prior to the maker of it, while all time is a creation, and every creation has taken its being from its creator?
112. I would, therefore, further examine our opponents, who esteem themselves so cunning, and have them make good the application of their theory to human existence, seeing that they use it to disparage the glory of God's Existence, and keep far away from any confession of an inscrutable mystery in the Divine Generation. I would have them find ground for their objection in the facts of human generation. Of God's Son they assert that before He was begotten He was not—that is to say, they say this of the Wisdom, the Power, the Word of God, Whose Generation knows nothing prior to itself. But if, as they would have us believe, there was a time when the Son existed not (the which it is blasphemy to affirm), then there was a time when God lacked the fullness of Divine Perfection, if afterwards He passed through a process of begetting a Son.
113. To show them, however, the weakness and transparency of their objection, though it has no real relation to any truth, divine or human, I will prove to them that men have existed before they were born. Else, let them show that Jacob, who while yet hidden in the secret chamber of his mother's womb supplanted his brother, had not been appointed and ordained, ere ever he was born; let them show that Jeremiah had not likewise been so, before his birth—Jeremiah, to whom the message comes: “Before I formed you in your mother's womb, I knew you; and before you came forth from the belly, I sanctified you, and appointed you for a prophet among the nations.” What testimony can we have stronger than the case of this great prophet, who was sanctified before he was born, and known before he was shaped?
114. What, again, shall I say of John, of whom his holy mother testifies that, while he yet lay in her womb, he perceived in spirit the presence of his Lord, and leaped for joy, as we remember it to be written, his mother saying: “For lo, as soon as the voice of the salutation entered mine ears, the babe leaped in my womb for joy.” Was he, then, who prophesied, in existence or not? Nay, surely he was— surely he was in being who worshipped his Maker; he was in being who spoke in his mother's womb. And so Elisabeth was filled with the spirit of her son, and Mary sanctified by the Spirit of hers, for thus you may find it recorded, that “the babe leaped in her womb, and Elisabeth was filled with the Holy Ghost.”
115. Consider the proper force of each word. Elisabeth was indeed the first to hear the voice of Mary, but John was first to feel His Lord's gracious Presence. Sweet is the harmony of prophecy with prophecy, of woman with woman, of babe with babe. The women speak words of grace, the babes move hiddenly, and as their mothers approach one another, so do they engage in mysterious converse of love; and in a twofold miracle, though in diverse degrees of honour, the mothers prophesy in the spirit of their little ones. Who, I ask, was it that performed this miracle? Was it not the Son of God, Who made the unborn to be?
116. Thus your objection fails of reconcilement with the truths of human existence— can it attain thereto with divine mysteries? What mean you by your principle that “before He was begotten He was not”? Was the Father engaged for some time in conception, so that certain epochs passed away before the Son was begotten? Was He, like women, in travail of birth, so that just this travail? What would you? Why seek we to pry into divine mysteries? The Scriptures tell me the necessary effects of the Divine Generation, not how it is done.
Source: On the Christian Faith (De fide) (New Advent)