Q. Why do we call Mary the “Mother of God?”
A. To understand, we have to look first at Jesus. From the very beginning, the Church has proclaimed that Jesus Christ is both God and Man. Jesus claimed for Himself the very name of God revealed to Moses, “I AM” (John 8:58), and He assumed divine prerogatives such as the forgiveness of sin (see Luke 5:18–26).
The Apostles testified to this reality. St. Thomas, for example, having known Jesus in His humanity, affirmed His divinity as well when he said to Him after His resurrection, “My Lord and my God!” (John 20:28).
St. John wrote in his Gospel that Jesus was “the Word” who “became flesh and dwelt among us,” and that this “Word was God” (John 1:1, 14). St. Paul taught that in Christ “dwells the whole fullness of the deity bodily” (Colossians 2:9).
When early Christians pondered these and other declarations of the apostolic witness, they wondered how exactly was Christ both human and divine? Was He, as some claimed, simply God and only appeared to be human? Was He, as others speculated, a human to whom God attached himself in a special way, dwelling inside Him? Or was He, as still others imagined, a kind of hybrid, partly human and partly divine?