III. When is the Liturgy Celebrated?

From The Catechism of the Catholic Church

1164
From the time of the Mosaic law, the People of God have observed fixed feasts,
beginning with Passover, to commemorate the astonishing actions of the Savior
God, to give him thanks for them, to perpetuate their remembrance, and to teach
new generations to conform their conduct to them. In the age of the Church,
between the Passover of Christ already accomplished once for all, and its
consummation in the kingdom of God, the liturgy celebrated on fixed days bears
the imprint of the newness of the mystery of Christ.

PART TWO: THE CELEBRATION OF THE CHRISTIAN MYSTERY

SECTION ONE THE SACRAMENTAL ECONOMY
- CHAPTER TWO THE SACRAMENTAL CELEBRATION OF THE PASCHAL MYSTERY
  - Article 1 CELEBRATING THE CHURCH’S LITURGY
    - III. When is the Liturgy Celebrated?

From The Catechism of the Catholic Church – rosary.team