Q. 1 Where does it say in the Bible that Mary is the mother of God?
A. 1 In the Gospel of Luke, filled with the Holy Spirit, [Lk. 1:41] Elizabeth exclaimed with a loud cry, [Lk. 1:42] "And why has this happened to me, that the mother of my Lord comes to me?" [Lk. 1:43]
Q. 2 How can that be? Can you explain it?
A. 2 In Matthew 1:18-25, we learn that the Blessed Virgin Mary was the mother of Jesus. In John 20:28, we learn that Jesus Christ is God.
Therefore, since Mary is the mother of Jesus and Jesus is God, then Mary is the Mother of God.
Q. 3 How can that be since God is eternal?
A. 3 Jesus Christ had two natures, the Divine nature and the human nature. Through the miraculous conception of Jesus in the womb of Mary, the eternal and immortal God (the Divine nature) took on a human nature in the womb of Mary.
To affirm this truth, the Council of Ephesus in 431 A.D. stated that Mary is truly the Mother of God because "according to the flesh" she gave birth to Jesus, who was truly God from the first moment of His conception. In this truth, "according to the flesh" is made clear that Mary is not the source of Jesus' divinity.