The celebration of Mass is an act of the whole assembly gathered for worship. In the Mass, the Church is joined to the action of Christ. We are joined to this divine action through Baptism, which incorporates us into the risen Christ. This action, which lies at “the center of the whole of Christian life” (General Instruction of the Roman Missal [GIRM], no. 16), is initiated not by us but by God acting in and through the Church as the Body of the risen Christ. The Liturgy is designed to bring about in all those who make up the worshiping assembly a “participation of the faithful, namely in body and in mind, a participation fervent with faith, hope, and charity” (GIRM, no. 18). To the extent that we are able to participate in this way, the work of redemption becomes personally effective for each of us. By such participation we make the actions and prayers of the Liturgy our own; we enter more fully into our personal communion with Christ’s redeem- ing act and perfect worship.
“In the celebration of Mass the faithful form a holy people, a people of God’s own possession and a royal Priesthood, so that they may give thanks to God and offer the unblemished sacrificial Victim not only by means of the hands of the Priest but also together with him and so that they may learn to offer their very selves. They should, moreover, take care to show this by their deep religious sense and their charity toward brothers and sisters who participate with them in the same celebration. . . .
Moreover, they are to form one body, whether in hearing the word of God, or in taking part in the prayers and in the singing, or above all by the common offering of the Sacrifice and by participat- ing together at the Lord’s table” (GIRM, nos. 95, 96).
The participation of each person in the Liturgy is important. Each person needs to do his or her part...
In addition to the ordained ministries, some roles in the Liturgy are exercised by lay people who place their time and talent at the service of the liturgical assembly as aco- lytes (altar servers), lectors, extraordinary ministers of Holy Communion, cantors, choir members, instrumentalists, leaders of song, and ushers. Others contribute their time and talent to planning and organizing the Liturgy; to keeping the church and the vestments, vessels, and appointments clean and well ordered; or to providing decorations that reflect the spirit of the liturgical feast or season.
From the USCCB on Participation in the Liturgy