True Mother of God
Despite being the Mother of God, Mary is not his mother in the sense that she is the source of her Son’s divinity or that she is greater than God.
In the year 428, on the eve of Christmas Eve in the Sofia Cathedral of Constantinople, the priest Proclus preached a sermon that would have many talk about it for ages. Among those present was a prominent place Nestorius, who was the Patriarch (Archbishop of the City).
According to tradition, Proclus said that Mary is Mother of God. But when the sermon was over, Nestorius stood on the pulpit and corrected the preacher, saying that he did not agree, because “Mary is the mother of the temple, but not of the God who dwells in the temple.”
At that moment something very unusual happened. A layman named Eusebius, a lawyer by profession who was accustomed to speaking in public. He rose from his seat and began to defend the faith. The faithful people were also outraged. They had always confessed Mary as Mother of God, we know that every day at the Angelus they recited the Sub tuum praesidium (Under your protection we take refuge, holy Mother of God).
The Patriarch was widely rejected by the people, and they began to boycott the events in which Nestorius was present, and they did not attend because they said that their bishop did not profess the Catholic faith.
Fix things at the Council
A couple of months later, Saint Cyril of Alexandria wrote a letter expressing his surprise that something basic about the faith was in doubt. Whether the Blessed Virgin should be called Mother of God, because that was the equivalent of asking if her son is God.
A great council was convened in Ephesus in the year 431, only three years after the conflict on that Christmas Eve. At the Council Mary is proclaimed Theotokos, Mother of God.
Against those who denied her, the Council of Ephesus proclaimed that: if anyone does not confess that the Emmanuel is truly God, and that therefore the Holy Virgin is the Mother of God, since she gave birth according to the flesh to the incarnate Word of God, let them be anathema.
Father Juan Carlos Vásconez