Catechism of the Catholic Church
1348 All gather together. Christians come together in one place for the Eucharistic assembly. At its head is Christ himself, the principal agent of the Eucharist. He is high priest of the New Covenant; it is he himself who presides invisibly over every Eucharistic celebration. It is in representing him that the bishop or priest acting in the person of Christ the head (in persona Christi capitis) presides over the assembly, speaks after the readings, receives the offerings, and says the Eucharistic Prayer. All have their own active parts to play in the celebration, each in his own way: readers, those who bring up the offerings, those who give communion, and the whole people whose "Amen" manifests their participation.
1349 The Liturgy of the Word includes "the writings of the prophets," that is, the Old Testament, and "the memoirs of the apostles" (their letters and the Gospels). After the homily, which is an exhortation to accept this Word as what it truly is, the Word of God, 175 and to put it into practice, come the intercessions for all men, according to the Apostle's words: "I urge that supplications, prayers, intercessions, and thanksgivings be made for all men, for kings, and all who are in high positions." 176
1350 The presentation of the offerings (the Offertory). Then, sometimes in procession, the bread and wine are brought to the altar; they will be offered by the priest in the name of Christ in the Eucharistic sacrifice in which they will become his body and blood. It is the very action of Christ at the Last Supper - "taking the bread and a cup." "The Church alone offers this pure oblation to the Creator, when she offers what comes forth from his creation with thanksgiving." 177 The presentation of the offerings at the altar takes up the gesture of Melchizedek and commits the Creator's gifts into the hands of Christ who, in his sacrifice, brings to perfection all human attempts to offer sacrifices.
1351 From the very beginning Christians have brought, along with the bread and wine for the Eucharist, gifts to share with those in need. This custom of the collection, ever appropriate, is inspired by the example of Christ who became poor to make us rich: 178
Those who are well off, and who are also willing, give as each chooses. What is gathered is given to him who presides to assist orphans and widows, those whom illness or any other cause has deprived of resources, prisoners, immigrants and, in a word, all who are in need. 179
1352 The anaphora: with the Eucharistic Prayer - the prayer of thanksgiving and consecration - we come to the heart and summit of the celebration:
In the preface, the Church gives thanks to the Father, through Christ, in the Holy Spirit, for all his works: creation, redemption, and sanctification. The whole community thus joins in the unending praise that the Church in heaven, the angels and all the saints, sing to the thrice-holy God.
1353 In the epiclesis, the Church asks the Father to send his Holy Spirit (or the power of his blessing 180) on the bread and wine, so that by his power they may become the body and blood of Jesus Christ and so that those who take part in the Eucharist may be one body and one spirit (some liturgical traditions put the epiclesis after the anamnesis).
In the institution narrative, the power of the words and the action of Christ, and the power of the Holy Spirit, make sacramentally present under the species of bread and wine Christ's body and blood, his sacrifice offered on the cross once for all.
1354 In the anamnesis that follows, the Church calls to mind the Passion, resurrection, and glorious return of Christ Jesus; she presents to the Father the offering of his Son which reconciles us with him.
In the intercessions, the Church indicates that the Eucharist is celebrated in communion with the whole Church in heaven and on earth, the living and the dead, and in communion with the pastors of the Church, the Pope, the diocesan bishop, his presbyterium and his deacons, and all the bishops of the whole world together with their Churches.
1355 In the communion, preceded by the Lord's prayer and the breaking of the bread, the faithful receive "the bread of heaven" and "the cup of salvation," the body and blood of Christ who offered himself "for the life of the world": 181
Because this bread and wine have been made Eucharist ("eucharisted," according to an ancient expression), "we call this food Eucharist, and no one may take part in it unless he believes that what we teach is true, has received baptism for the forgiveness of sins and new birth, and lives in keeping with what Christ taught." 182
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.