Q. If the Catholic Church has such good reasons for calling Mary the Mother of God then why did the Protestants stop using this title?
A. It is not known when the Protestant churches dropped this title for Mary or by what authority they did so since all of the principle reformers vigorously affirmed and defended this doctrine.
Martin Luther: “In this work whereby she was made the Mother of God, so many and such good things were given her that no one can grasp them…Not only was Mary the mother of Him who is born in Bethlehem but of Him who, before, the world, was eternally born of the Father, from a Mother in time and at the same time man and God” (Weimer, The Works of Luther, English translation by Pelikan, Concordia, St. Souis, V7, P572)
Christ . . . was the only Son of Mary, and the Virgin Mary bore no children besides Him . . . “brothers” really means “cousins” here, for Holy Writ and the Jews always call cousins brothers. (Sermons on John, chapters 1-4, 1537-39)
He, Christ, our Savior, was the real and natural fruit of Mary’s virginal womb . . . This was without the cooperation of a man, and she remained a virgin after that. (Ibid.)
God says . . . : “Mary’s Son is My only Son.” Thus Mary is the Mother of God.(Ibid.)
God did not derive his divinity from Mary; but it does not follow that it is therefore wrong to say that God was born of Mary, that God is Mary’s Son, and that Mary is God’s mother . . . She is the true mother of God and bearer of God . . . Mary suckled God, rocked God to sleep, prepared broth and soup for God, etc. For God and man are one person, one Christ, one Son, one Jesus, not two Christs . . . just as your son is not two sons . . . even though he has two natures, body and soul, the body from you, the soul from God alone.(On the Councils and the Church, 1539)
John Clavin: “I cannot be denied that God in Choosing and destining Mary to be the Mother of His Son, granted her the highest
honor…Elizabeth calls mary Mother of the Lord, because the unity of the person in the two natures of Christ was such that she could have said that the mortal man engendered in the womb of Mary was at the same time the eternal God.” (Calvin Opera, Corpus Reformatorum, Braunschweig-Berlin, 1863-1900, V. 45 p 348, 35)
Ulrich Zwingli: “It was given to her what belongs to no creature, that in the flesh she sould bring forth the Son of God.” (Zwingli Opera, Corpus Reformatorum, Berlin, 1905, in Evang. Luc., Op. comp., V6,1 P. 639