How can God have a mother?! The question is a sincere one. While this question comes from a simple misunderstanding of the meaning of the word Theotokos, the answer is of great importance.
Mary was the Mother of Jesus. That is universally accepted. But then, who was Jesus? Was He God or Man or both? Was Mary the Theotokos (the Greek term theotokos means ‘God-bearer’), meaning, did she bear God?
While we celebrate the Feast of the Dormition of the Theotokos on August 15th, it is good to take a step back and ask a more fundamental question. Why is such importance given to Mary, the Mother of Jesus, and why is she called the Theotokos?
“Many Protestants will lose sleep over any significant role being awarded to Mary other than her being a virgin and the mother of Jesus. They may not appreciate either the title “Mother of God” But the claim that Mary is the Mother of God says as much about Jesus’ identity as it does about Mary’s status.”1
In the fifth century, Nestorius, the Archbishop of Constantinople, began to publicly preach, “That which had been born of Mary was the man Jesus, in whom, the Divine had taken residence and dwelt as in a temple.”2 In effect, he was saying Mary had not given birth to the God-man, and therefore should not be called Theotokos, but Christotokos (Birthgiver of Christ).
This claim, which came to be known as the Nestorian heresy, struck at the very root of Christian faith that Jesus Christ was God, “For if from Mary only a man was born, then it was not God Who suffered for us, but a man.” 3>
Christians believed that in the womb of Mary, God and man were joined. She was the one who served, as it were, as the ladder for the Son of God, Who descended from heaven. That is why in the Divine Liturgy, we say “incarnate of the Holy Spirit and the Virgin Mary.” To strike a blow at her is to strike Christianity at the root, to destroy its very foundation.
Thus it was decided to convene an ecumenical council, at which hierarchs, gathered from the ends of the world, should decide whether the faith preached by Nestorius was Orthodox.
The decision of the Church at the Third Council of Ephesus was clear. It clearly expressed its faith that Christ, born of the Virgin, is the true God Who became man; and inasmuch as Mary gave birth to the perfect Man Who was at the same time perfect God, She rightly should be revered as Theotokos.
“He who does not confess Immanuel to be true God and therefore the Holy Virgin to be Theotokos, because She gave birth in the flesh to the Word Who is from God the Father and Who became flesh, let him be anathema (separated from the Church)” (First Anathema of St. Cyril of Alexandria).
So when we revere St Mary as the Theotokos, we are affirming that Jesus’ divinity and humanity are not separate. Rather there is one person, who has two natures: the divine and the human. Jesus was the God-man. Holy, Blessed, Mary was the God-bearer, the Theotokos.
2St John Maximovitch (paraphrased)
3St John Maximovitch (paraphrased)