16 You said in your unreason, and you are still repeating today, ignorant that your wisdom is a defiance of God, “As to such phrases as from Him, and from the womb, and I went out from the Father and have come,” I ask you, Are these phrases, or are they not, words of God? They certainly are His; and, since they are spoken by God about Himself, we are bound to accept them exactly as they were spoken. Concerning the phrases themselves, and the precise force of each, we shall speak in the proper place.
For the present I will only put this question to the intelligence of every reader; When we see From Himself, are we to take it as equivalent to “From some one else,” or to “From nothing,” or are we to accept it as the truth? It is not “From some one else,” for it is From Himself; that is, His Godhead has no other source than God. It is not “From nothing,” for it is From Himself; a declaration of the nature from which His birth is. It is not “Himself,” but From Himself; a statement that They are related as Father and Son.
And next, when the revelation From the womb is made, I ask whether we can possibly believe that He is born from nothing, when the truth of His birth is clearly indicated in terms borrowed from bodily functions. It is not because He has bodily members, that God records the generation of the Son in the words, I bore You from the womb before the morning star. He uses language which assists our understanding to assure us that His Only-begotten Son was ineffably born of His own true Godhead.
His purpose is to educate the faculties of men up to the knowledge of the faith, by clothing Divine verities in words descriptive of human circumstances. Thus, when He says, From the womb, He is teaching us that His Only-begotten was, in the Divine sense, born, and did not come into existence by means of creation out of nothing. And lastly, when the Son said, I went forth from the Father and have come, did He leave it doubtful whether His Divinity were, or were not, derived from the Father? He went out from the Father; that is, He had a birth, and the Father, and no other, gave Him that birth. He bears witness that He, from Whom He declares that He came forth, is the Author of His being. The proof and interpretation of all this shall be given hereafter.
Source: On the Trinity (New Advent)