CONSTITUTION ON 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.