In the Encyclical Mediator Dei, Pope Pius XII states that it “is not a cold and lifeless representation of the events of the past, or a simple … record of a former age. [The liturgical year] is rather Christ Himself who is ever living in His Church. The liturgical year should thus be understood as a constant renewal of the work of salvation which Christ accomplishes in history. As she journeys through this temporal cycle, the Church remains in contact with the Lord’s redemptive action, so that all the faithful may be filled with His grace (cf. SC, 102c).
Saint John Paul II, in the Apostolic Letter Dies Domini (31 May 1998) teaches that Sunday is the day of the Lord, the day of the Church, the day of man and, finally, the “day of days”. .. To sanctify Sunday, it is fundamental to celebrate the Eucharist. Listening to the Word and partaking of the Body of Christ entail, according to the Council Fathers, the coming together in unum (cf. SC, 106), that is, the joyful gathering of the faithful. In this assembly, the Christian community makes visible its communion with the Lord and bears witness to its belonging to Christ and its fidelity to the Church. This assembly cannot be substituted by a solely virtual presence, nor can it be reduced to a merely passive gathering. The liturgical assembly is in fact fulfilled through the active participation of brothers and sisters, called together to “thank God who ‘has begotten them again, through the resurrection of Jesus Christ from the dead, unto a living hope’” (1 Pet 1:3) (ibid.).
The liturgical year, punctuated by Sundays, has an interesting history, in which the faith and devotion of the Church are interwoven. Indeed, from as early as the second century AD, the celebration of the weekly Easter was joined by that of the annual Easter, the “most solemn festival” (SC, 102), extending over the most joyful period of fifty days, culminating in Pentecost, and prepared for by the season of Lent with its penitential character (cf. SC, 109). The development of the Christmas cycle, which took place later and was modelled on the Paschal cycle, has made it possible to relive the mysteries of the Incarnation of the Word of God, of His birth and of His manifestation to the world. The Church then incorporated into the various times the veneration of the Blessed Virgin Mary, “joined by an inseparable bond to the saving work of her Son” (SC, 103), and “the memory of the martyrs and the other saints” who “sing God’s perfect praise in heaven and offer prayers for us” (SC, 104).