THAT THE BLESSED VIRGIN MARY is the Mother of God means that the child—conceived in her womb by the power of the Holy Spirit, carried in her body for nine months, and born into this world—is God. As such, this title of Mary highlights the pivotal truth of the Church’s Faith: that God has, in Jesus Christ, accepted a human nature, chosen to be born into this world as we have all been born into this world, and has lived a real, human life.
In doing so, God has accepted the full implication of what it means to be human, including the experiences of suffering and death.
When we identify the Blessed Virgin Mary as the Mother of God, the emphasis is only secondarily on her; it is primarily about Christ. Mary being referred to as the Mother of God tells us that Jesus Christ is God and was always God. Christ did not “turn” into God, and calling Christ God is not just some kind of projection by which we make Jesus of Nazareth someone very important. That Jesus is really and truly God is a fact. God accepting a human nature in Christ and living a real human life is not just a story we tell that is all symbol, myth and legend; it is all true and it really happened.
The Incarnation of God in Christ is the singular and privileged way by which God reveals himself to the world. We see in Christ with the greatest clarity possible who God is and what he is all about.
Fr. Steve Grunow, The Mystery of Mary, Mother of God
Original in Word on Fire Blog, wordonfire.org, January 1, 2018