Theotokos - The God Bearer

Yesterday Jan, 1st was the Solemnity of the Mother of God. A day the Church uses to remind the faithful where Mary stands in the economy of our salvation. Few Marian doctrines create more controversy than the way we refer to Mary as the Mother of God. Yet this doctrine is probably one of the easiest to defend in terms of its early historicity and writings of the Church Fathers. The early Church made this declaration at the Council of Ephesus in the early fifth century to combat the heresies that were circulating regarding the nature of Christ (again). How and why did the Church declare Mary, the Mother of God? Was it to detract from God's glory and raise Mary to a divine status? No, actually quite the opposite. By declaring this doctrine, the Church affirmed and protected the divinity of Christ! See the following for an explanation.
From CUF website:

"Nestorius, a monk of Antioch who in 428 became the patriarch of Constantinople, publicly preached that Christ was not God, but that God only dwelt in Him as in a temple. In other words, he taught that there were two persons in Christ, and thus Mary was Christotokos (Mother of Christ), but not Theotokos (Mother of God). “Christotokos” became the watchword of the Nestorians.
The true Christian teaching was championed by Saint Cyril, who was the patriarch of Alexandria. Saint Cyril not only strenuously defended the Catholic faith among his own flock, but he also addressed letters to Nestorius in a charitable, brotherly attempt to lead him back to the Catholic faith.
When these attempts failed, Cyril appealed to Pope Celestine, writing that “the ancient custom of the Churches admonishes us that matters of this kind should be communicated to Your Holiness.”[4] Celestine condemned the teaching of Nestorius and appointed Cyril as his representative for settling the controversy.
Meanwhile, Emperor Theodosius convoked an ecumenical council at Ephesus to facilitate the resolution of the dispute. Under the presidency of Saint Cyril, and with full papal approval and authority, the Council condemned the false teaching of Nestorius and fully affirmed Christ’s divinity:
Scripture does not say that the Word associated the person of a man with Himself, but that He was made flesh. But when it is said that the Word was made flesh, that means nothing else but that He partook of flesh and blood, even as we do; wherefore, He made our body His own, and came forth man, born of a woman, at the same time without laying aside His Godhead, or His birth from the Father; for in assuming flesh He still remained what He was.[5]
The decision of the Council of Ephesus is a classic example of how authentic Marian doctrine flows from and will always protect and safeguard authentic teachings concerning the Person of Christ. By proclaiming that Mary is Theotokos, the Church is affirming that Mary is truly a mother, thus affirming Jesus’ humanity. By affirming that she is the Mother of God, the Church is not only affirming Jesus’ divinity, but also the union of Jesus’ human and divine natures in His one divine Person."


"Early Christian Tradition, particularly the liturgy, bears witness to the Christian belief that Mary is the Mother of God. In the oldest profession of the Christian faith, the Apostles’ Creed (cf. Catechism, no. 194), the faithful for nearly two millennia have professed their faith in “Jesus Christ, His Only Son, Our Lord, who was conceived by the Holy Spirit, born of the Virgin Mary.” The ancient Marian prayer Sub tuum praesidium (“We fly to thy protection ... “), which dates back to the third century, explicitly addresses Mary as “Mother of God.”
Mary’s divine motherhood is richly attested to in the writings of the Church Fathers. For example, Saint Irenaeus (d. 202) wrote, “The Virgin Mary, ... being obedient to His word, received from an angel the glad tidings that she would bear God.”[1]
Saint Ephrem of Syria (d. 373), in his poetic Hymns of the Nativity, authored the following:
In the womb of Mary, the Infant was formed, who from eternity is equal to the Father. . . .
The Virgin became a Mother while preserving her virginity; And though still a virgin she carried a Child in her womb; And the handmaid and work of His Wisdom became the Mother of God.[2]
Saint Athanasius (d. 373), in his treatise On the Incarnation of the Word of God and Against the Arians, wrote:
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 -- so that those who are in the first place born here below might have a second birth from on high, that is, of God.[3]
These are just a handful of the many patristic references to this Marian teaching during the first four centuries of Christianity. Of course, after the dogmatic definition of the Council of Ephesus in 431 (see below), this teaching was firmly established as part of the deposit of faith entrusted to the Church (cf. 1 Tim. 6:20)."

Scripture, as well, supports the doctrine with Elizabeth's acclamation: "And who am I that the Mother of my Lord should come to me?"

Jesus is God, the second person of the Trinity. Mary was Jesus' mother, therefore Mary is the Mother of God, the Incarnate.