Mass is celebration of the Eucharist, the principal and indeed essential worship service of the majority of Christians. Eastern Orthodox Churches call this service the Divine Liturgy. The Articles of Religion of the Anglican Church employ the term "the Lordís Supper" (article XXVIII), but the expression most used by Anglicans is "Holy Communion", a term the Roman Catholic Church applies to a particular aspect of the Eucharist, forbidding lay extraordinary ministers of Holy Communion to be called ministers of the Eucharist (Redemptionis Sacramentum, 156).
Etymologically, the word "Mass" is derived from the phrase with which the celebration concludes in Latin, Ite, missa est, where "missa" is late Latin for earlier "missio", so that the phrase means: "You may go, this is the dismissal." Because of its origin in the Latin language, the word "Mass" is normally used only of the eucharistic liturgy as celebrated in the Latin rites.
No attempt is made here to present the theology of the Mass, as viewed by different Churches. For that, the reader is referred to the respective catechisms. What follows is merely a brief summary of the outward form of Mass.
In its article on Roman Catholicism (within the section "The Modern Denominations"), the Encyclopaedia Britannica (1998 CD edition) states that the Church "is not primarily an organization, nor is it a school of doctrine. It is the place where God approaches humanity through grace and where humanity approaches God through worship. Hence the focus of Roman Catholic piety is the Eucharist, which is both a sacrament and a sacrifice. Other forms of corporate worship and of private devotion radiate from this point of central focus."
Official liturgical books used at Mass
The Roman Missal contains the prayers and rubrics of the Mass. In the United States and Canada, the English translation of this book is called the Sacramentary, a term that the Holy See has said should be abandoned for this book.
Other Western Churches may not have a specific book for their celebration of the Eucharist. In the Anglican Communion, the form to be used is given within the Book of Common Prayer.
The Mass Lectionary presents passages from the Bible arranged in the order for reading at each day's Mass. Before the Second Vatican Council, the then far less numerous Scripture readings in use were included in the Roman Missal.
A Book of the Gospels is recommended for the reading from the Gospels, but the Lectionary is sometimes used instead.
Structure of Mass
Within the fixed structure outlined below, the text of several prayers and of the Scripture readings varies from day to day.
An exchange of greetings between the priest and the congregation follows an entrance hymn and the priest's veneration of the altar. Then, in the Penitential Rite, all reflect on the thoughts and words, deeds and omissions by which they have fallen short of the Christian code of conduct and pray for mercy in the Confiteor and Kyrie eleison (Greek for "Lord, have mercy"), or in an alternative prayer, and the priest invokes God's forgiveness on all.
On Sundays, except during penitential seasons, and on important feast days, the Gloria, a joyful song of praise, is next sung. Then the priest says the variable collect, concluding the introductory part of the Mass
Liturgy of the Word
Two or, on Sundays and on the major feast days known as solemnities, three readings from the Bible are heard, and a psalm with a repeated response is sung or recited after the first reading. When there are three such readings, the first is from the Old Testament, except in Eastertide, when it is taken from the Acts of the Apostles or the Book of Revelation, known also as the Apocalypse, and the second is from the letters of the apostles, mostly St. Paul's. The final reading is from one of the Gospels, the first four books of the New Testament: (Matthew, Mark, Luke, John). These four books are given special respect, and the reading from them is reserved for a deacon or priest and is preceded by ceremonies that generally include singing Alleluia or another acclamation and perhaps incensing the Book of the Gospels or Lectionary. The whole congregation is also obliged to stand during the reading of the Gospel.
The Sunday readings are arranged in a three-year cycle, so that a particular passage of Scripture returns only after three years. On weekdays outside of Lent and Advent, a two-year arrangement governs the first reading, while the Gospel readings form a single-year cycle.
A homily, a sermon by a priest or deacon elucidating some aspect of the readings or another part of the liturgy, is obligatory on Sundays and Holy Days of Obligation, and is recommended on other days.
On Sundays and solemnities the Creed is recited by all. The formula traditionally used is the Nicene Creed, but use of the shorter Apostles Creed is now permitted.
The Liturgy of the Word concludes with the Intercessions, called also the Prayer of the Faithful or the Universal Prayer. The last of these names recalls the recommendation in 1 Tim 2:1-2 that prayers be offered for all. There is no fixed formula for this: after an introduction by the priest, a number of intentions are proposed, to each of which the congregation responds with a short prayer; the priest then concludes with a general prayer.
Liturgy of the Eucharist
This begins with the preparation of the altar and the gifts. Bread on a paten and wine mixed with a little water in a chalice are placed on the altar. The bread must be wheaten. In the tradition of the Latin Church, it is in the form of a thin white wafer of unleavened bread. In anticipation of its change into the body of the victim of the sacrifice that the liturgy makes sacramentally present, it is called a host, from the Latin word "hostia", meaning "victim". This preparatory part of the Liturgy of the Eucharist concludes with a variable prayer over the bread and wine thus set apart.
The eucharistic prayer, also called the canon of the Mass, or (especially when speaking of the liturgies of Eastern Christianity) the anaphora, is the solemn center of the Mass. Accordingly, in the dialogue with which it begins, the priest follows up the usual initial greeting, "The Lord be with you", with the exhortation, "Lift up your hearts", and then introduces the great theme of thanksgiving, the Greek word for which is "eucharistia" (eucharist): "Let us give thanks to the Lord our God."
There follows the variable preface of the eucharistic prayer, elaborating on particular motives, associated perhaps with the feast of the day, for giving thanks to God, and leading to the Sanctus, the chant pictured in Isaiah 6:3 and Revelation 4:8 as being offered as praise in heaven.
The eucharistic prayer culminates in the commemoration of Jesus' actions at the Last Supper. According to Roman Catholic doctrine, at the repetition of his words, and by the power of the Holy Spirit, the bread and wine become his body and blood, a change that has been described as transubstantiation. This moment is known as the consecration. The consecration is considered an act of transubstantiation in some other denominations as well, but others call it consubstantiation, which indicates that the body and blood has entered the bread and wine but they remain at the same time bread and wine.
The eucharistic prayer also recalls the death and resurrection of Jesus and his final glorious return, intercedes for living and dead and expresses fellowship with the whole Church in heaven and on earth.
The congregation participates in the opening dialogue and the Sanctus acclamation, and sings or speaks an acclamation after the consecration and an Amen after the final doxology.
The "Lord's Prayer" ("Pater Noster" or "Our Father") is followed by an elaboration of its last petition and a doxology. Then the priest says a prayer for peace and unity and may invite those present to offer each other the sign of peace in some simple way. Next, to the singing or recitation of the "Agnus Dei" ("Lamb of God"), comes the breaking of the consecrated bread. Then the priest receives communion and gives communion also to the congregation under the appearance of at least bread ("in one kind") or of both bread and wine ("in both kinds"), to the accompaniment of a hymn or of the variable communion antiphon. If the numbers receiving communion are large, lay extraordinary ministers of holy communion may assist the priest or priests. A variable postcommunion prayer then concludes the communion rite.
Announcements may then be made, after which the Mass as a whole ends with a blessing by the priest and a phrase of dismissal based on the Latin "Ite, missa est".
Time of celebration of Mass
Before the liturgical reforms of Pope Pius XII and the Second Vatican Council, it was forbidden, except on Christmas night, to begin Mass more than one hour before dawn or more than one hour after midday. There are no longer any time limits. While Roman Catholics could previously fulfil their obligation to attend a Sunday Mass only on the morning of Sunday itself, they may now do so on Saturday evening (generally taken to mean not before 4 p.m.) or at any time on Sunday. Most parish churches offer this possibility on Saturday evening, a much smaller number on Sunday evening.