"Parts of the Mass" - I

The following is part 1 (of 3) of “the parts of the Mass”, as explained in the General Instruction of the Roman Missal (the official rules and details of the Latin Rite Mass), and abbreviated for purposes of this site. Please click on the orange arrow next to the title of this post for the full text.
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I. The General Structure of the Mass

27. At Mass—that is, the Lord's Supper—the People of God is called together, with a priest presiding and acting in the person of Christ, to celebrate the memorial of the Lord, the Eucharistic Sacrifice. For this reason Christ's promise applies in an outstanding way to such a local gathering of the holy Church: "Where two or three are gathered in my name, there am I in their midst" (Mt 18:20). For in the celebration of Mass, in which the Sacrifice of the Cross is perpetuated, Christ is really present in the very liturgical assembly gathered in his name, in the person of the minister, in his word, and indeed substantially and continuously under the eucharistic species.

28. The Mass is made up, as it were, of two parts: the Liturgy of the Word and the Liturgy of the Eucharist. These, however, are so closely interconnected that they form but one single act of worship. For in the Mass the table both of God's word and of Christ's Body is prepared, from which the faithful may be instructed and refreshed. There are also certain rites that open and conclude the celebration.

III. The Individual Parts of the Mass

The Entrance
47. After the people have gathered, the Entrance chant begins as the priest enters with the deacon and ministers. The purpose of this chant is to open the celebration, foster the unity of those who have been gathered, introduce their thoughts to the mystery of the liturgical season or festivity, and accompany the procession of the priest and ministers.

Greeting of the Altar and of the People Gathered Together
49. When they reach the sanctuary, the priest, the deacon, and the ministers reverence the altar with a profound bow. As an expression of veneration, moreover, the priest and deacon then kiss the altar itself; as the occasion suggests, the priest also incenses the cross and the altar.

50. When the Entrance chant is concluded, the priest stands at the chair and, together with the whole gathering, makes the Sign of the Cross. Then he signifies the presence of the Lord to the community gathered there by means of the Greeting. By this Greeting and the people's response, the mystery of the Church gathered together is made manifest.

The Act of Penitence
51. Then the priest invites those present to take part in the Act of Penitence, which, after a brief pause for silence, the entire community carries out through a formula of general confession. The rite concludes with the priest's absolution, which, however, lacks the efficacy of the Sacrament of Penance.

The Kyrie Eleison
52. After the Act of Penitence, the Kyrie is always begun, unless it has already been included as part of the Act of Penitence. Since it is a chant by which the faithful acclaim the Lord and implore his mercy, it is ordinarily done by all, that is, by the people and with the choir or cantor having a part in it.

The Gloria
53. The Gloria is a very ancient and venerable hymn in which the Church, gathered together in the Holy Spirit, glorifies and entreats God the Father and the Lamb. The text of this hymn may not be replaced by any other text. The Gloria is intoned by the priest or, if appropriate, by a cantor or by the choir; but it is sung either by everyone together, or by the people alternately with the choir, or by the choir alone. If not sung, it is to be recited either by all together or by two parts of the congregation responding one to the other. It is sung or said on Sundays outside the Seasons of Advent and Lent, on solemnities and feasts, and at special celebrations of a more solemn character.

The Collect
54. Next the priest invites the people to pray. All, together with the priest, observe a brief silence so that they may be conscious of the fact that they are in God's presence and may formulate their petitions mentally. Then the priest says the prayer which is customarily known as the Collect and through which the character of the celebration is expressed. In accordance with the ancient tradition of the Church, the collect prayer is usually addressed to God the Father, through Christ, in the Holy Spirit, and is concluded with a trinitarian, that is to say the longer ending, in the following manner:

If the prayer is directed to the Father: Per Dominum nostrum Iesum Christum Filium tuum, qui tecum vivit et regnat in unitate Spiritus Sancti, Deus, per omnia saecula saeculorum;

If it is directed to the Father, but the Son is mentioned at the end: Qui tecum vivit et regnat in unitate Spiritus Sancti, Deus, per omnia saecula saeculorum;

If it is directed to the Son: Qui vivis et regnas cum Deo Patre in unitate Spiritus Sancti, Deus, per omnia saecula saeculorum. The people, uniting themselves to this entreaty, make the prayer their own with the acclamation Amen. There is always only one collect used in a Mass.