St. Cyril of Alexandria

Oversimplified

• Patriarch of Alexandria (c. 376–444) and the great theologian of the Incarnation, who defended the title Theotokos — "God-bearer" — for the Virgin Mary.
• The leading voice at the Third Ecumenical Council (Ephesus, 431), which condemned Nestorius and confirmed that the one born of Mary is truly God the Word made flesh.

Summary

Cyril's life work was to guard the unity of Christ. When Nestorius, patriarch of Constantinople, objected to calling Mary Theotokos and seemed to divide the incarnate Lord into two persons, Cyril answered that there is one Christ, one Son — God the Word who made human nature truly his own.[^1] To deny Mary the title Theotokos, he argued, is finally to deny that the child in her womb is God.

The Council of Ephesus

At Ephesus in 431 the Church affirmed Cyril's teaching and the title Theotokos, a landmark in the confession of The Incarnation. His formula of the one incarnate person shaped the definition of Chalcedon twenty years later and remains foundational for Orthodox Christology.[^2] See also The Trinity, Ecumenical Councils.

[^1]: St. Cyril, On the Unity of Christ and the Letters to Nestorius. [^2]: The Council of Ephesus (431); his influence on the Council of Chalcedon (451).