Whether it is celebrated by the humblest parish priest or as it will be this afternoon by the pope himself, the mass is the most important rite of worship for Roman Catholics.

In it, the faithful come together to renew their beliefs, acknowledge their sins, implore forgiveness, and seek grace -- or divine help -- to live a better life.

For Catholics, the source of salvation is the Eucharist, the communion wafer that is served during the mass. Once blessed by a priest, the Eucharist is belived by Catholics to mystically become Christ's body. By taking communion, then, Catholics believe they are reunited with Christ.

Today's mass on the Mass will be celebrated by Pope John Paul II with bishops and the cardinals of the Washington, Baltimore, Wilmington, Arlington and Richmond dioceses. As the mass gets under way the celebrants, dressed in their special liturgical robes, will approach the altar area in a procession and will venerate, or kiss, the altar.

The service will proceed as follows:

The Greeting. The pope will greet the assembled worshipers with the traditional opening words of the liturgy: "Peace be with you." The faithful respond, " . . . and also with you," an exchange that symbolizes that the church is gathered for worship.

Penitential Rite. The pope, bishops and the people recite a confession acknowledging their shortcomings and imploring God's mercy.

Glorida and prayer. An ancient hymn of praise to God is followed by a spoken prayer by the chief celebrant. The faithful then make the prayer theim own by responding "Amen."

Liturgy of the Word. Three Bible readings. Selections from the Old Testament and the portion of the New Testament, known as the epistles, may be read by lay men or women. The gospel is read by a priest or ordained deacon.

Homily. Pope John Paul will deliver a homily, or sermon, on the theme of the family.

Profession of faith. The people and the pope together recite this ancient creed, a reassertion of and recommitment to the fundamental teachings of the faith.

General intercession. This is a prayer imploring God's help for the church, the nation, its civil, and religious authorities. In addition, individuals may ask the entire congregation to pray for specific persons or causes. After each petition the entire congregation responds.

Liturgy of the Eucharist. This is the beginning of the most solemn part of the mass. A prayer of thanksgiving is proclaimed by the pope as the chief celebrant. Then gifts of break and wine to be used in the communion service are brought to the altar by lay persons, along with other offerings.

The choir sings an offertory song as the gifts are brought forward and the altar is infused with incense to symbolize the prayers rising to God, the celebrants -- the pope and bishops -- wash their hands as an expression of the desire for inward purification.

A series of formal prayers, including the most solemn prayer of thanksgiving and sanctification follow. In a special prayer, the pope and bishops, together, invoke the Holy Spirit and ask that the gifts of bread and wine become the actual body and blood of Christ.

The chief celebrant recites Christ's words of the Last Supper as recorded in the gospel, recounting how he urged his followers to reenact that event, which has become the heart of the mass.

After a series of solemn prayers, the worshipers greet each other with handshakes or embraces to signify both unity of the church and Christian love.

After this, priests and deacons fan out among the gathered faithful to distribute the consescrated communion bread, proclaiming "the body of Christ," to each person who received. At the Mall mass, specially invited guests will receive communion directly from the pope.

After concluding prayers and a blessing the worshippers are dismissed.