This may be the most significant move of its kind since St. John Paul added Divine Mercy Sunday.
From Vatican News:
Pope Francis has decreed that the ancient devotion to the Blessed Virgin Mary, under the title of Mother of the Church, be inserted into the Roman Calendar.
The liturgical celebration, B. Mariæ Virginis, Ecclesiæ Matris, will be celebrated annually as a Memorial on the day after Pentecost.
In a decree released on Saturday by the Congregation for Divine Worship and the Discipline of the Sacraments, Cardinal Robert Sarah, its Prefect, said the Pope’s decision took account of the tradition surrounding the devotion to Mary as Mother of the Church.
He said the Holy Father wishes to promote this devotion in order to “encourage the growth of the maternal sense of the Church in the pastors, religious and faithful, as well as a growth of genuine Marian piety”The decree reflects on the history of Marian theology in the Church’s liturgical tradition and the writings of the Church Fathers.
It says Saint Augustine and Pope Saint Leo the Great both reflected on the Virgin Mary’s importance in the mystery of Christ.
“In fact the former [St. Augustine] says that Mary is the mother of the members of Christ, because with charity she cooperated in the rebirth of the faithful into the Church, while the latter [St. Leo the Great] says that the birth of the Head is also the birth of the body, thus indicating that Mary is at once Mother of Christ, the Son of God, and mother of the members of his Mystical Body, which is the Church.”
The decree says these reflections are a result of the “divine motherhood of Mary and from her intimate union in the work of the Redeemer.”
The full text of the decree is at the link.