During the first few centuries of the Church, many debated the role of Mary, and bishops argued about her motherhood. It took the Council of Ephesus in 431 to put many of these matters to rest and affirm her title as Mary, Mother of God.
St. Cyril of Alexandria was present at this council and composed this beautiful prayer at the end of his sermon, which is included in the Office of Readings for the feast of the Dedication of St. Mary Major.