102 Holy Mother Church is conscious that she must celebrate the saving work of her divine Spouse by devoutly recalling it on certain days throughout the course of the year. Every week, on the day which she has called the Lord's day, she keeps the memory of the Lord's resurrection, which she also celebrates once in the year, together with His blessed passion, in the most solemn festival of Easter. Within the cycle of a year, moreover, she unfolds the whole mystery of Christ, from the incarnation and birth until the ascension, the day of Pentecost, and the expectation of blessed hope and of the coming of the Lord. Recalling thus the mysteries of redemption, the Church opens to the faithful the riches of her Lord's powers and merits, so that these are in some way made present for all time, and the faithful are enabled to lay hold upon them and become filled with saving grace.
Source: Sacrosanctum Concilium (Vatican.va)