Mary is the Mother of God
“After this, we receive the doctrine of the resurrection from the dead, of which Jesus Christ our Lord became the first-fruits; Who bore a Body, in truth, not in semblance, derived from Mary the mother of God in the fullness of time sojourning among the race, for the remission of sins: who was crucified and died, yet for all this suffered no diminution of His Godhead.” Alexander of Alexandria, Epistle to Alexander, 12 (A.D. 324).
“Many, my beloved, are the true testimonies concerning Christ. The Father bears witness from heaven of His Son: the Holy Ghost bears witness, descending bodily in likeness of a dove: the Archangel Gabriel bears witness, bringing good tidings to Mary: the Virgin Mother of God bears witness: the blessed place of the manger bears witness.” Cyril of Jerusalem, Catechetical Lectures, X:19 (c. A.D. 350).
“And the Angel on his appearance, himself confesses that he has been sent by his Lord; as Gabriel confessed in the case of Zacharias, and also in the case of Mary, bearer of God.” Athanasius, Orations III, 14(A.D. 362).
“Just as, in the age of Mary the mother of God, he who had reigned from Adam to her time found, when he came to her and dashed his forces against the fruit of her virginity as against a rock, that he was shattered to pieces upon her, so in every soul which passes through this life in the flesh under the protection of virginity, the strength of death is in a manner broken and annulled, for he does not find the places upon which he may fix his sting.” Gregory of Nyssa, On Virginity, 14 (A.D. 370).
“He reshaped man to perfection in Himself, from Mary the Mother of God through the Holy Spirit.” Epiphanius, The man well-anchored, 75 (A.D. 374).
“Let, then, the life of Mary be as it were virginity itself, set forth in a likeness, from which, as from a mirror, the appearance of chastity and the form of virtue is reflected. From this you may take your pattern of life, showing, as an example, the clear rules of virtue: what you have to correct, to effect, and to hold fast. The first thing which kindles ardour in learning is the greatness of the teacher. What is greater than the Mother of God?” Ambrose, Virginity, II:6 (c. A.D. 378).
“If anyone does not believe that Holy Mary is the Mother of God, he is severed from the Godhead.” Gregory of Nazianzus, To Cledonius, 101 (A.D. 382).
“To the question: ‘Is Mary the bearer of Man, or the bearer of God?’ we must answer: ‘Of Both.’” Theodore of Mopsuestia, The Incarnation, 15 (ante A.D. 428).
“And so, you say, O heretic, whoever you may be, who deny that God was born of the Virgin, that Mary the Mother of our Lord Jesus Christ ought not to be called Theotocos, i.e., Mother of God, but Christotocos, i.e., only the Mother of Christ, not of God. For no one, you say, brings forth what is anterior in time. And of this utterly foolish argument whereby you think that the birth of God can be understood by carnal minds, and fancy that the mystery of His Majesty can be accounted for by human reasoning, we will, if God permits, say something later on. In the mean while we will now prove by Divine testimonies that Christ is God, and that Mary is the Mother of God.” John Cassian, The Incarnation of Christ, II:2 (A.D. 430).
“But since the Holy Virgin brought forth after the flesh God personally united to the flesh, for this reason we say of her that she is Theotokos, not as though the nature of the Word had its beginning of being from the flesh, for he was in the beginning, and the Word was God, and the Word was with God…but, as we said before, because having personally united man’s nature to himself…” Cyril of Alexandria, To Nestorius, Epistle 17:11 (A.D. 430).
“If anyone will not confess that the Emmanuel is very God, and that therefore the Holy Virgin is the Mother of God (Theotokos), inasmuch as in the flesh she bore the Word of God made flesh [as it is written, ‘The Word was made flesh’: let him be anathema.” Council of Ephesus, Anathemas Against Nestorius, I (A.D. 430).
“For by the singular gift of Him who is our Lord and God, and withal, her own son, she is to be confessed most truly and most blessedly–The mother of God ‘Theotocos,’ but not in the sense in which it is imagined by a certain impious heresy which maintains, that she is to be called the Mother of God for no other reason than because she gave birth to that man who afterwards became God, just as we speak of a woman as the mother of a priest, or the mother of a bishop, meaning that she was such, not by giving birth to one already a priest or a bishop, but by giving birth to one who afterwards became a priest or a bishop. Not thus, I say, was the holy Mary ‘Theotocos,’ the mother of God, but rather, as was said before, because in her sacred womb was wrought that most sacred mystery whereby, on account of the singular and unique unity of Person, as the Word in flesh is flesh, so Man in God is God.” Vincent of Lerins, Commonitory for the Antiquity and Universality of the Catholic Faith, 15 (A.D. 434).
“So then He was both in all things and above all things and also dwelt in the womb of the holy Mother of God, but in it by the energy of the incarnation.” John Damascene, Source of Knowledge, III:7 (A.D. 743).