Council of Ephesus

(Gest. Conc. Eph.) Wherefore in one place divine Scripture calls Him the Son, in another the Word, in another the Brightness of the Father; names severally meant to guard against blasphemy. For, forasmuch as thy son is of the same nature with thyself, the Scripture wishing to show that the Substance of the Father and the Son is one, sets forth the Son of the Father, born of the Father, the Only-Begotten. Next, since the terms birth and son, convey the idea of passibleness, therefore it calls the Son the Word, declaring by that name the impassibility of His Nativity. But inasmuch as a father with us is necessarily older than his son, lest thou shouldest think that this applied to the Divine nature as well, it calls the Only-Begotten the Brightness of the Father; for brightness, though arising from the sun, is not posterior to it. Understand then that Brightness, as revealing the coeternity of the Son with the Father; Word as proving the impassibility of His birth, and Son as conveying His consubstantiality.

(P. iii. Hom. Theod. Ancyr. de Nat. Dom.) The discourse which we utter, which we use in conversation with each other, is incorporeal, imperceptible, impalpable; but clothed in letters and characters, it becomes material, perceptible, tangible. So too the Word of God, which was naturally invisible, becomes visible, and that comes before us in tangible form, which was by nature incorporeal.

Herein we must beware of the error of Nestorius, who thus speaks; "When Divine Scripture is to speak either of the birth of Christ which is of the Virgin Mary, or His death, it is never seen to put God, but either, Christ, or Son, or Lord; since these three are significative of the two natures, sometimes of this, sometimes of that, and sometimes of both this and that together. And here is a testimony to this, Jacob begot Joseph the husband of Mary, of whom was born Jesus, who is called Christ. For God the Word needed not a second birth of a woman."