Why is Mary called the Mother of God?

Mary is called Mother of God (Theotokos) because she is the mother of Jesus Christ, who is one Divine Person with two natures, human and divine. Since she truly bore the Son of God in her womb, and the child she bore is God himself, she is rightly called Mother of God — a title defined at the Council of Ephesus in 431.

The title 'Mother of God' does not mean Mary is the source or origin of God's divine nature, which is eternal. It means that the person she conceived and bore, Jesus Christ, is truly God the Son incarnate. Because Mary is the mother of a real, single Person — not merely of a human nature that God later assumed — she is the mother of that Person who is God (CCC 495).

Scriptural Foundation

Scripture affirms that the child born of Mary is divine. At the Annunciation, the angel Gabriel tells Mary that the child she will bear 'shall be called the Son of God' (Luke 1:35). When Mary visits her, Elizabeth, filled with the Holy Spirit, greets her as 'the mother of my Lord' (Luke 1:43) — 'Lord' being the title used throughout the New Testament for the divine Christ. St. John's Gospel identifies this same child as the eternal Word who 'was God' and 'was made flesh' (John 1:1, 14), and St. Paul writes that 'God sent his Son, made of a woman' (Galatians 4:4), showing that the one born of Mary is God's own Son.

The Council of Ephesus and the Unity of Christ

In the early fifth century, the heresy of Nestorianism proposed that Mary bore only the human nature of Christ, and that a distinct divine Person somehow joined itself to that human person later, so that Mary should be called only 'Christotokos' (Mother of Christ) rather than 'Theotokos' (Mother of God). The Church rejected this at the Council of Ephesus in 431, teaching that Jesus Christ is one Divine Person with two natures united without confusion or division. Since there are not two sons in Christ, one divine and one human, but one and the same Son, Mary's motherhood necessarily extends to the whole Person she bore — who is God (CCC 466). This dogma safeguards not primarily an honor to Mary but the truth about who Jesus Christ is.

Why This Title Matters

Calling Mary the Mother of God protects the central mystery of the Incarnation: that the eternal Son of God truly became man, taking flesh from the Virgin Mary, so that our humanity could be joined to divinity for our salvation (CCC 466, 495). Far from exalting Mary above Christ, the title exalts Christ by insisting that he who was born of Mary is truly and fully God. The Church continues to honor this truth liturgically, celebrating the Solemnity of Mary, Mother of God, each January 1st.