In the first decades of the fifth century, when Alexandria and Constantinople were continuing their feud over their respective positions in the Church and in the Empire, Nestorius, the bishop of Constantinople (r. 428–431), made known his refusal to honor Mary, Christ’s mother, with the traditional title of Theotokos. He claimed that the one born from Mary is not the Logos Himself, but merely the “man” in whom the eternal Logos of God came to dwell. Thus, Mary could not properly be called “Theotokos,” which means “the one who gave birth to God,” but only either “Christotokos,” meaning “the one who gave birth to Christ,” or “anthropotokos,” meaning ‘the one who gave birth to a man’—i.e., the man Jesus, to whom the Logos was joined.
Saint Cyril, Bishop of Alexandria (r. 412–444), with the active support of Pope Celestine of Rome, forcefully rejected the teaching of Nestorius, claiming that it is indeed proper to call Mary Theotokos since the one born from her “according to the flesh” is none other than the divine Logos of God. The only-begotten Son of God was “begotten of the Father before all ages”; and He it was “Who for us men and for our salvation came down from Heaven, and was incarnate of the Holy Spirit and the Virgin Mary, and became man” (The Nicene Creed). Thus, the Son of God and the Son of Mary is one and the same Son.