Today’s Catechism sections explore the communal nature of the liturgy. Supporting material comes from the Pastoral Constitution, “Sacrosanctum Concilium”.
THE SACRAMENTAL CELEBRATION OF THE PASCHAL MYSTERY
1135 The catechesis of the liturgy entails first of all an understanding of the sacramental economy (Chapter One). In this light, the innovation of its celebration is revealed. This chapter will therefore treat of the celebration of the sacraments of the Church. It will consider that which, through the diversity of liturgical traditions, is common to the celebration of the seven sacraments. What is proper to each will be treated later. This fundamental catechesis on the sacramental celebrations responds to the first questions posed by the faithful regarding this subject:
- Who celebrates the liturgy?
- How is the liturgy celebrated?
- When is the liturgy celebrated?
- Where is the liturgy celebrated?
CELEBRATING THE CHURCH'S LITURGY
I. Who Celebrates?
1136 Liturgy is an "action" of the whole Christ (Christus totus). Those who even now celebrate it without signs are already in the heavenly liturgy, where celebration is wholly communion and feast
The celebrants of the heavenly liturgy
1137 The book of Revelation of St. John, read in the Church's liturgy, first reveals to us, "A throne stood in heaven, with one seated on the throne": "the Lord God."1 It then shows the Lamb, "standing, as though it had been slain": Christ crucified and risen, the one high priest of the true sanctuary, the same one "who offers and is offered, who gives and is given."2 Finally it presents "the river of the water of life . . . flowing from the throne of God and of the Lamb," one of most beautiful symbols of the Holy Spirit.3
1138 "Recapitulated in Christ," these are the ones who take part in the service of the praise of God and the fulfillment of his plan: the heavenly powers, all creation (the four living beings), the servants of the Old and New Covenants (the twenty-four elders), the new People of God (the one hundred and forty-four thousand),4 especially the martyrs "slain for the word of God," and the all-holy Mother of God (the Woman), the Bride of the Lamb,5 and finally "a great multitude which no one could number, from every nation, from all tribes, and peoples and tongues."6
1139 It is in this eternal liturgy that the Spirit and the Church enable us to participate whenever we celebrate the mystery of salvation in the sacraments.
The celebrants of the sacramental liturgy
1140 It is the whole community, the Body of Christ united with its Head, that celebrates. "Liturgical services are not private functions but are celebrations of the Church which is 'the sacrament of unity,' namely, the holy people united and organized under the authority of the bishops. Therefore, liturgical services pertain to the whole Body of the Church. They manifest it, and have effects upon it. But they touch individual members of the Church in different ways, depending on their orders, their role in the liturgical services, and their actual participation in them."7 For this reason, "rites which are meant to be celebrated in common, with the faithful present and actively participating, should as far as possible be celebrated in that way rather than by an individual and quasi-privately."8
1141 The celebrating assembly is the community of the baptized who, "by regeneration and the anointing of the Holy Spirit, are consecrated to be a spiritual house and a holy priesthood, that . . . they may offer spiritual sacrifices."9 This "common priesthood" is that of Christ the sole priest, in which all his members participate:10
Mother Church earnestly desires that all the faithful should be led to that full, conscious, and active participation in liturgical celebrations which is demanded by the very nature of the liturgy, and to which the Christian people, "a chosen race, a royal priesthood, a holy nation, a redeemed people," have a right and an obligation by reason of their Baptism.11
1142 But "the members do not all have the same function."12 Certain members are called by God, in and through the Church, to a special service of the community. These servants are chosen and consecrated by the sacrament of Holy Orders, by which the Holy Spirit enables them to act in the person of Christ the head, for the service of all the members of the Church.13 The ordained minister is, as it were, an "icon" of Christ the priest. Since it is in the Eucharist that the sacrament of the Church is made fully visible, it is in his presiding at the Eucharist that the bishop's ministry is most evident, as well as, in communion with him, the ministry of priests and deacons.
1143 For the purpose of assisting the work of the common priesthood of the faithful, other particular ministries also exist, not consecrated by the sacrament of Holy Orders; their functions are determined by the bishops, in accord with liturgical traditions and pastoral needs. "Servers, readers, commentators, and members of the choir also exercise a genuine liturgical function."14
1144 In the celebration of the sacraments it is thus the whole assembly that is leitourgos, each according to his function, but in the "unity of the Spirit" who acts in all. "In liturgical celebrations each person, minister or layman, who has an office to perform, should carry out all and only those parts which pertain to his office by the nature of the rite and the norms of the liturgy."15
1187 The liturgy is the work of the whole Christ, head and body. Our high priest celebrates it unceasingly in the heavenly liturgy, with the holy Mother of God, the apostles, all the saints, and the multitude of those who have already entered the kingdom.
1188 In a liturgical celebration, the whole assembly is leitourgos, each member according to his own function. The baptismal priesthood is that of the whole Body of Christ. But some of the faithful are ordained through the sacrament of Holy Orders to represent Christ as head of the Body.
The Pastoral Constitution, “Sacrosanctum Concilum” explains the communal nature of the Sacred Liturgy.
26. Liturgical services are not private functions, but are celebrations of the Church, which is the "sacrament of unity," namely, the holy people united and ordered under their bishops 
Therefore liturgical services pertain to the whole body of the Church; they manifest it and have effects upon it; but they concern the individual members of the Church in different ways, according to their differing rank, office, and actual participation.
27. It is to be stressed that whenever rites, according to their specific nature, make provision for communal celebration involving the presence and active participation of the faithful, this way of celebrating them is to be preferred, so far as possible, to a celebration that is individual and quasi-private.
This applies with especial force to the celebration of Mass and the administration of the sacraments, even though every Mass has of itself a public and social nature.
28. In liturgical celebrations each person, minister or layman, who has an office to perform, should do all of, but only, those parts which pertain to his office by the nature of the rite and the principles of liturgy.
29. Servers, lectors, commentators, and members of the choir also exercise a genuine liturgical function. They ought, therefore, to discharge their office with the sincere piety and decorum demanded by so exalted a ministry and rightly expected of them by God's people.
Consequently they must all be deeply imbued with the spirit of the liturgy, each in his own measure, and they must be trained to perform their functions in a correct and orderly manner.
1 ⇒ Rev 4:2, 8; ⇒ Isa 6:1; cf. ⇒ Ezek 1:26-28.
2 ⇒ Rev 5:6; Liturgy of St. John Chrysostom, Anaphora; cf. ⇒ Jn 1:29; ⇒ Heb 4:14-15; ⇒ 10:19-2.
3 ⇒ Rev 22:1; cf. ⇒ 21:6; ⇒ Jn 4:10-14.
4 Cf. ⇒ Rev 4- 5; ⇒ 7:1-8; ⇒ 14:1; ⇒ Isa 6:2-3.
5 ⇒ Rev 6:9-11; ⇒ Rev 21:9; cf. ⇒ 12.
6 ⇒ Rev 7:9.
7 SC 26.
8 SC 27.
9 LG 10; cf. ⇒ 1 Pet 2:4-5.
10 Cf. LG 10; 34; PO 2.
11 SC 14; Cf. ⇒ 1 Pet 2:9; ⇒ 2:4-5.
12 ⇒ Rom 12:4.
13 Cf. PO 2; 15.
14 SC 29.
15 SC 28.