St. Cyril of Alexandria
St. Cyril is one of the great Greek fathers of the Church. He was chosen by divine Providence to be the shield and champion of the Church against Nestorius, who denied the unity of person in Christ. If this heresy had succeeded, Mary would not be called the Mother of God.
Cyril was born in 376 at Alexandria, Egypt and became partriarch archbishop of his birthplace in 412. He presided over the Ecumenical Council of Ephesus which defined the inseparable unity of the divine and human natures of Christ, and thus the appropriateness of invoking the Blessed Virgin Mary under the title of “Theotokos” or Mother of God. He died in 444AD.
Prayer in Honor of Mary, Mother of God
Hail, Mary, Mother of God, venerable treasure of the whole universe, lamp that is never extinguished, crown of virginity, support of the true faith, indestructible temple, dwelling of him whom no place can contain, O Mother and Virgin! Through you all the holy Gospels call blessed the one whom comes in the name of the Lord.
Hail, Mother of God. You enclosed under your heart the infinite God whom no space can contain. Through you the Most Holy Trinity is adored and glorified, the priceless cross is venerated throughout the universe. Through you the heavens rejoice, and the angels and archangels are filled with gladness. Through you the demons are banished, and the tempter fell from heaven. Through you the fallen human race is admitted to heaven.
Hail, Mother of God. Through you kings rule, and the only-begotten Son of God has become a star of light to those who were sitting in darkness and in the shadow of death.
~Saint Cyril of Alexandria, Bishop and Doctor