32 In the order of our defence, as I have arranged it in my mind, this has seemed the most convenient place for proving that, thirdly, the Apostles believed our Lord Jesus Christ to be the Son of God, not merely in name but in nature, not by adoption but by birth. It is true that there remain unmentioned many and most weighty words of God the Only-begotten concerning Himself, in which the truth of His Divine birth is set so clearly forth as to silence any whisper of objection. Yet since it would be unwise to burden the reader's mind with an accumulation of evidence, and ample proof has been already given of the genuineness of His birth, I will hold back the remainder of His utterances till later stages of our enquiry. For we have so arranged the course of our argument that now, after hearing the Father's witness and the Son's self-revelation, we are to be instructed by the Apostles' faith in the true and, as we must confess, the truly born Son of God. We must see whether they could find in the words of the Lord, I went forth from God, any other meaning than this, that there was in Him a birth of the Divine nature.
Source: On the Trinity (New Advent)