This claim repeats an ancient error already held by the Nestorian Schism in the 5th century. However, the faith of the Church is clear: Mary is Theotokos, Mother of God, because the one she gave birth to is true God and true man.
The Gospel shows Mary not only as a humble servant, but as the one who gives birth to “Immanuel – God with us” (Isa 7:14; Mt 1:23). Elizabeth calls her “the mother of my Lord” (Lk 1:43). Since “Lord” (Kyrios) in the Jewish context is the name of God (cf. LXX), Scripture already testifies to Mary’s divine motherhood.
The Council of Ephesus (431) defined dogmatically: “If anyone does not confess that Emmanuel is truly God, and therefore the holy Virgin is the Mother of God (Theotokos), because she gave birth in the flesh to the Word of God made flesh: let him be excluded.” (DH 252). This is not about Mary herself, but about correct Christology. Whoever calls Mary only “Christ-bearer” separates Christ into two persons – a human Jesus and the divine Logos. But Scripture teaches: “The Word became flesh” (Jn 1:14). The person whom Mary gave birth to is one single person: the God-man.
The Church Fathers confirm this. Athanasius of Alexandria (†373) says: “The Word took flesh from Mary, the Mother of God” (Oratio contra Arianos II,70). Cyril of Alexandria, the great defender of Ephesus, wrote: “Whoever does not confess Mary as Mother of God separates Christ into two sons.” (Epistola ad Nestorium).
Mary is therefore Mother of God not because she is the origin of the divinity, but because she brought the human nature of the eternal Son into the world. Her title protects the truth of the Incarnation.