Of all Mary's titles, none is greater than Mother of God because it signifies her intimate, loving and exulted union with God who became incarnate in her womb.
The angel of the Lord declared unto Mary.
And she conceived by the Holy Spirit.
This is the moment when Mary became the Mother of God.
In the fifth century Nestorius, patriarch of Constantinople, taught that in Jesus there is a human and a divine person and that Mary gave birth only to the human person and that she received passively the divine person, therefore, she could not be called Theotokos, Mother of God. The Council of Ephesus (431A.D.) condemned Nestorius as a heretic.
And the Word was made flesh.
And dwelt among us.
In 436 A.D. the Council of Chalcedon defined the nature of Christ as both human and divine united in one person, thereby affirming that when Mary conceived, carried and gave birth to the Second Person of the Trinity in his human nature she became the Mother of God.
In what sense is Mary truly the Mother of God?
A mother is such because she contributes to the substance of the nature of the child, carries and gives birth not only to a human nature but to a person. Mary is not the Mother of God in the sense as being the source of his divine nature but because she conceived, carried in her womb and gave birth to a divine person, Jesus Christ, in his humanity.
Mary rejoiced in her dignity as the Mother of God as she humbly exclaimed to Elizabeth: " My being proclaims the greatness of the Lord, my spirit finds joy in God my savior, For he has looked upon his servant in her lowliness; all ages to come shall call me blessed." (Lk 1:46-48). This prophecy is indeed evident today in the many churches dedicated to her honor and in all the Catholic Churches as the mysteries of Mary are depicted in stained glass windows and the Ave Maria (Hail Mary) is on the lips of countless Catholics honoring her as exulted above all the angels and saints.
benedicta tu in mulieribus,
et benedictus fructus ventris tui, Jesus.
ora pro nobis peccatoribus,
nunc et in hora
mortis nostrae. Amen.
Ccourtesy of Harry & Dorret Goodwin