Theotókos (Θεοτόκος) is one of the title given to Mary. Theotókos in Greek is God-bearer, the one who gives birth to God, and Mother of God Incarnate. In the Council of Ephesus in 431 A.D. decreed that Mary is the Mother of God. Since Jesus is God and human. When Protestants bring this topic up, in their mind they think this refers to God the Father and thinking that Mary is Mother of God from eternity. However this title is only referring to the Incarnation of Jesus. To summarize it Mary is called Mother of God Incarnate. Even before the legalization of Christianity and the Council of Ephesus, the early Church believed that Mary is the Theotókos. Before the Council of Ephesus, their was debates about the title of Mary. There were two titles, Christotokos and Theotókos. Mary is Theotokos because her son, Jesus, is one person who is both God and man. Since Jesus is God Incarnate and through the Virgin birth Jesus came into flesh. So it is right to call Mary the Theotókos.
Does this title, Mother of God, imply that Mary is in some way superior to God? Of course not! Mary is clearly a creature. But like all mothers, Mary gave birth to a person. In her case it was a divine Person, the Second Person of the Blessed Trinity. However, in giving birth to her Divine Son she was not giving birth to his divinity, which existed from all eternity.
† The Early Church Fathers †
Irenaeus
"The Virgin Mary, being obedient to his word, received from an angel the glad tidings that she would bear God"- Against Heresies, 5:19:1 (A.D. 189).
Hippolytus
"[T]o all generations they [the prophets] have pictured forth the grandest subjects for contemplation and for action. Thus, too, they preached of the advent of God in the flesh to the world, his advent by the spotless and God-bearing (theotokos) Mary in the way of birth and growth, and the manner of his life and conversation with men, and his manifestation by baptism, and the new birth that was to be to all men, and the regeneration by the laver [of baptism]"-Discourse on the End of the World 1 (A.D. 217).
Gregory the Wonderworker
"For Luke, in the inspired Gospel narratives, delivers a testimony not to Joseph only, but also to Mary, the Mother of God, and gives this account with reference to the very family and house of David"-Four Homilies 1 (A.D. 262).
"It is our duty to present to God, like sacrifices, all the festivals and hymnal celebrations; and first of all, [the feast of] the Annunciation to the holy Mother of God, to wit, the salutation made to her by the angel, ‘Hail, full of grace!’" (ibid., 2).
Peter of Alexandria
"They came to the church of the most blessed Mother of God, and ever-virgin Mary, which, as we began to say, he had constructed in the western quarter, in a suburb, for a cemetery of the martyrs"- The Genuine Acts of Peter of Alexandria (A.D. 305).
"We acknowledge the resurrection of the dead, of which Jesus Christ our Lord became the firstling; he bore a body not in appearance but in truth derived from Mary the Mother of God"-Letter to All Non-Egyptian Bishops 12 (A.D. 324).
Methodius
"While the old man [Simeon] was thus exultant, and rejoicing with exceeding great and holy joy, that which had before been spoken of in a figure by the prophet Isaiah, the holy Mother of God now manifestly fulfilled"-Oration on Simeon and Anna 7 (A.D. 305).
"Hail to you forever, you virgin Mother of God, our unceasing joy, for unto you do I again return. . . . Hail, you fount of the Son’s love for man. . . . Wherefore, we pray you, the most excellent among women, who boast in the confidence of your maternal honors, that you would unceasingly keep us in remembrance. O holy Mother of God, remember us, I say, who make our boast in you, and who in august hymns celebrate your memory, which will ever live, and never fade away" (ibid., 14).
Cyril of Jerusalem
"The Father bears witness from heaven to his Son. The Holy Spirit bears witness, coming down bodily in the form of a dove. The archangel Gabriel bears witness, bringing the good tidings to Mary. The Virgin Mother of God bears witness"-Catechetical Lectures 10:19 (A.D. 350).
Ephraim the Syrian
"Though still a virgin she carried a child in her womb, and the handmaid and work of his wisdom became the Mother of God"-Songs of Praise 1:20 (A.D. 351).
Athanasius
"The Word begotten of the Father from on high, inexpressibly, inexplicably, incomprehensibly, and eternally, is he that is born in time here below of the Virgin Mary, the Mother of God"-The Incarnation of the Word of God 8 (A.D. 365).
Epiphanius of Salamis
"Being perfect at the side of the Father and incarnate among us, not in appearance but in truth, he [the Son] reshaped man to perfection in himself from Mary the Mother of God through the Holy Spirit"-The Man Well-Anchored 75 (A.D. 374).
Ambrose of Milan
"The first thing which kindles ardor in learning is the greatness of the teacher. What is greater than the Mother of God? What more glorious than she whom Glory Itself chose?" -The Virgins 2:2[7] (A.D. 377).
Gregory of Nazianz
"If anyone does not agree that holy Mary is Mother of God, he is at odds with the Godhead"-Letter to Cledonius the Priest 101 (A.D. 382).
Jerome
"As to how a virgin became the Mother of God, he [Rufinus] has full knowledge; as to how he himself was born, he knows nothing"-Against Rufinus 2:10 (A.D. 401).
"Do not marvel at the novelty of the thing, if a Virgin gives birth to God"-Commentaries on Isaiah 3:7:15 (A.D. 409).
Theodore of Mopsuestia
"When, therefore, they ask, ‘Is Mary mother of man or Mother of God?’ we answer, ‘Both!’ The one by the very nature of what was done and the other by relation"-The Incarnation 15 (A.D. 405).
Cyril of Alexandria
"I have been amazed that some are utterly in doubt as to whether or not the holy Virgin is able to be called the Mother of God. For if our Lord Jesus Christ is God, how should the holy Virgin who bore him not be the Mother of God?"-Letter to the Monks of Egypt 1 (A.D. 427).
"This expression, however, ‘the Word was made flesh’ [John 1:14], can mean nothing else but that he partook of flesh and blood like to us; he made our body his own, and came forth man from a woman, not casting off his existence as God, or his generation of God the Father, but even in taking to himself flesh remaining what he was. This the declaration of the correct faith proclaims everywhere. This was the sentiment of the holy Fathers; therefore they ventured to call the holy Virgin ‘the Mother of God,’ not as if the nature of the Word or his divinity had its beginning from the holy Virgin, but because of her was born that holy body with a rational soul, to which the Word, being personally united, is said to be born according to the flesh"-First Letter to Nestorius (A.D. 430).
"And since the holy Virgin corporeally brought forth God made one with flesh according to nature, for this reason we also call her Mother of God, not as if the nature of the Word had the beginning of its existence from the flesh"-Third Letter to Nestorius (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, inasmuch as in the flesh she bore the Word of God made flesh [John 1:14]: let him be anathema" (ibid.).
John Cassian
"Now, you heretic, you say (whoever you are who deny that God was born of the Virgin), that Mary, the Mother of our Lord Jesus Christ, cannot be called the Mother of God, but the Mother only of Christ and not of God—for no one, you say, gives birth to one older than herself. And concerning this utterly stupid argument . . . let us prove by divine testimonies both that Christ is God and that Mary is the Mother of God"-On the Incarnation of Christ Against Nestorius 2:2 (A.D. 429).
"You cannot then help admitting that the grace comes from God. It is God, then, who has given it. But it has been given by our Lord Jesus Christ. Therefore the Lord Jesus Christ is God. But if he is God, as he certainly is, then she who bore God is the Mother of God" (ibid., 2:5).
Council of Ephesus
"We confess, then, our Lord Jesus Christ, the only begotten Son of God, perfect God and perfect man, of a rational soul and a body, begotten before all ages from the Father in his Godhead, the same in the last days, for us and for our salvation, born of Mary the Virgin according to his humanity, one and the same consubstantial with the Father in Godhead and consubstantial with us in humanity, for a union of two natures took place. Therefore we confess one Christ, one Son, one Lord. According to this understanding of the unconfused union, we confess the holy Virgin to be the Mother of God because God the Word took flesh and became man and from his very conception united to himself the temple he took from her"-Formula of Union (A.D. 431).
Vincent of Lerins
"Nestorius, whose disease is of an opposite kind, while pretending that he holds two distinct substances in Christ, brings in of a sudden two persons, and with unheard-of wickedness would have two sons of God, two Christs,—one, God, the other, man; one, begotten of his Father, the other, born of his mother. For which reason he maintains that Saint Mary ought to be called, not the Mother of God, but the Mother of Christ"-The Notebooks 12[35] (A.D. 434).
Mary is the mother of Jesus.
Jesus is truly God.
Therefore, Mary is the mother of God.
Where is it in the Bible?