January 1, Solemnity of Mary, Mother of God
This feast is the octave of Christmas. In the modern Roman Calendar only Christmas and Easter enjoy the privilege of an octave. According to the 1962 Missal of Bl. John XXIII the Extraordinary Form of the Roman Rite, today is the Solemnity of Circumcision of Our Lord.
"Mary, the all-holy ever-virgin Mother of God, is the masterwork of the mission of the Son and the Spirit in the fullness of time. For the first time in the plan of salvation and because his Spirit had prepared her, the Father found the dwelling place where his Son and his Spirit could dwell among men. In this sense the Church's Tradition has often read the most beautiful texts on wisdom in relation to Mary. Mary is acclaimed and represented in the liturgy as the "Seat of Wisdom."
— Catechism of the Catholic Church 721
A plenary indulgence may be gained by reciting or singing the hymn Veni Creator Spiritus on the first day of the year. This hymn is traditionally sung for beginnings of things, calling on the Holy Spirit before endeavoring something new.