The Feast of the Solemnity of Mary, Mother of God is a liturgical feast of the Blessed Virgin Mary honoring her divine motherhood to Jesus Christ. It is celebrated by the Catholic Church on the 1st of January, the Octave (8 of 12th) Day of Christmas. In some Catholic countries, this day is designated as a Holy Day of Obligation.
The feast was celebrated in the East before it was in the West, but by the 5th century it was celebrated in France and Spain on the Sunday before Christmas. In Rome, even before the 7th century, 1 January was used as a celebration of the Maternity of the Blessed Virgin Mary. In the 13th and 14th centuries, the Feast of the Circumcision of Christ had come to replace the Marian feast on 1 January. The celebration of the Feast of the Circumcision on 1 January was expanded to the entire Catholic Church in 1570 when Pope Pius V promulgated the Missal.
In 1914, the feast of the “Maternity of the Blessed Virgin Mary” was established in Portugal, occurring on 11 October. In 1931, this feast was extended to the entire Catholic Church by Pope Pius XI and maintained on 11 October. Following the Second Vatican Council in 1974, Pope Paul VI removed the Feast of the Circumcision of Christ from the liturgical calendar, and replaced it with the feast of the “Solemnity of Mary, Mother of God.” In the Extraordinary form of the Roman Rite, Catholics continue to celebrate this feast day with the old name “The Maternity of the Blessed Virgin Mary” on 11 October, and 1 January is the Octave Day of the Nativity of the Lord.
The feast is a celebration of Mary’s motherhood of Jesus.
The title “Mother of God” is a western derivation from the Greek: Theotokos, the God-bearer. The term was adopted at the First Council of Ephesus as a way to assert the Divinity of Christ, from which it follows that what is predicated of Christ is predicated of God. So, if Mary is the mother of Jesus, she is the Mother of God. Therefore, the title “Mother of God” and the “Solemnity of Mary, Mother of God”, which celebrates her under this title, are at once both Mariological and Christological.