The Feast of the Maternity of the Blessed Virgin Mary was instituted in 1932 by Pope Pius XI. The Feast is a double of the second class and so is celebrated today, in white vestments. The Feast of the Maternity of the Holy Mother of God was instituted in honor of the fifteenth centenary of the Council of Ephesus where Mary was defined as Mother of God.
The Church celebrates the Divine Maternity, which was conferred on a mere creature, and which made her the co-operatrix with Jesus in the great work of man's salvation.
But it is today, that we, the children of the Roman Church, must pour forth all the love of our hearts for the Virgin-Mother, and rejoice with her in the exceeding happiness she feels at having given birth to her and our Lord. During Advent, we contemplated her as pregnant with the world's salvation; we proclaimed the glory of that Ark of the New Covenant, whose chaste womb was the earthly paradise, chosen by the King of Ages for His dwelling-place. Now, she has brought Him forth, the Infant-God; she adores Him, Him who is her Son. She has the right to call Him, her Child; and He, God as He is, calls her in strictest truth, his Mother. Let us not be surprised, therefore, at the enthusiasm and profound respect, wherewith the Church extols the Blessed Virgin, and her prerogatives.
Mary is the Mother of God!--It is the mystery, whose fulfillment the world, without knowing it, was awaiting for four thousand years. It is the work, which, in God's eyes, was incomparably greater than that of the creation of a million new worlds, for such a creation would cost Him nothing; He has but to speak, and all whatsoever He wills is made. But, that a creature should become Mother of God, He has had, not only to suspend the laws of nature by making a Virgin Mother, but also to put Himself in a state of dependence upon the happy creature He chose for His Mother. He had to give her rights over Himself, and contract the obligation of certain duties towards her. He had to make Her his Mother, and Himself her Son.