The Solemnity of Mary, Mother of God is a liturgical feast of the Blessed Virgin Mary, celebrated on 1 January, the Octave Day of Christmas. In the United States this day is considered a holy day of obligation.
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 Theotokos was adopted at the Council of Ephesus as a way to affirm the Divinity of Christ, from which it follows that what applies to Christ also applies to God. So, since 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 Mariological and Christological.
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 came to replace the Marian feast on 1 January.
The celebration of the Feast of the Circumcision on 1 January was expanded to the entire Roman Catholic Church in 1570 when Pope Pius V promulgated the Roman 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 Roman 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 Christmas, the Nativity of the Lord