Theotokos - Mother of God

I just wanted to share this from Fr Robert Barron's book 'Catholicism'.

It explains the reason why Mary is called 'Theotokos'  meaning 'God bearer' or 'the one who bore God' and as we more commonly say 'Mother of God'.

THEOTOKOS

As he was dying on the cross, Jesus looked to his mother and to the disciple whom he loved, and he said to Mary, “Woman, behold, your son,” and then to John, “Behold, your mother” (Jn 19:26–27). We are told that “from that hour the disciple took her into his own home” (Jn 19:27). This text supports an ancient tradition that the apostle John took Mary with him when he traveled to Ephesus in Asia Minor and that both ended their days in that city. Indeed, on the top of a high hill overlooking the Aegean Sea, just outside Ephesus, there is a modest dwelling that tradition holds to be the house of Mary. In the year 431 a great council of the church met in the cathedral of Ephesus in order to adjudicate a bitter dispute about the identity of Jesus, but the debate became focused on a technical question in regard to Mary, namely, whether she could legitimately be called Theotokos, or Mother of God. The council fathers were trying to understand Jesus more accurately, precisely by teasing out the implications of the conversation that took place between the girl of Nazareth and the angel of the Annunciation.
The background for this council meeting at Ephesus is fascinating. We have to begin by returning, once more, to that conversation at Caesarea-Philippi, when Jesus asked the disciples, “Who do people say that I am?” That question, especially in light of the resurrection, haunted the minds of the members of the ancient church, and the best intellects of the time strove to answer it accurately. Important steps were taken at the Council of Nicaea in 325, when Jesus was declared to be homoousios (one in being) with the Father, and at the Council of Constantinople in 381, when that teaching was reiterated. But in the 420s a controversy arose over the teaching of Nestorius, who was the patriarch of Constantinople and a much-revered theological figure. Influenced by the school of Antioch, which placed a great stress on the humanity of Jesus, Nestorius said that in Christ two distinct persons—one divine and one human—come together in a kind of moral union. This meant that Mary, who was responsible only for the human element in Jesus, could be called Christotokos (mother of Christ) but not Theotokos (mother of God). In fact, Nestorius argued, the use of that latter title would be the height of blasphemy, since it would imply that a mere human being had a sort of primacy over God. Cyril, the bishop of Alexandria, and another theological heavyweight, was so outraged by Nestorius’s position that he called the bishop of Constantinople a heretic. The ecumenical council of Ephesus was summoned in order to resolve this controversy. After much deliberation during the summer of 431, the council fathers taught that Jesus ought not to be understood as a human person with a particularly intense relationship to the person of God, for that would make him a kind of supreme saint but not the incarnate Son of God. And if he were not himself divine, he would require a saviour as much as anyone else. Rather it was decided that in the unity of his person both divinity and humanity come together. And this meant, they concluded, that Nestorius was wrong to deny Mary the title Theotokos, for if Jesus was divine and Mary was the mother of Jesus, then Mary could and should be called the Mother of God. To Nestorius’s point about the blasphemous nature of this description, the council fathers said that Mary is not the mother of Jesus’s divinity, but the mother of Jesus, who is, in fact, divine.
The declaration of Mary as Mother of God is an instance of the general principle that whatever is said about Mary is meant not so much to draw attention to her as to throw light on Christ. To say that Mary is the Mother of God is to insist on the density of the claim that God truly became human, one of us, bone of our bone and flesh of our flesh. As Archbishop Fulton J. Sheen commented, “Mary is like the moon, for her light is always the reflection of a higher light.”

Barron, Robert (2011-11-01). Catholicism (Enhanced Edition) (Kindle Locations 1445-1448). Image. Kindle Edition.