Many of the texts of the Mass in both the Roman and Byzantine Rites are set to music, which is preferred to as Gregorian chant in the Western Church. The chants contained in each mass can be separated into distinct groups initially: those that are constant for each and every Mass, or the Ordinary, and those that change according to the feast day being celebrated on the calendar, or the Propers.
The chants of the Ordinary of the Mass are most straightforward in their reforms, and probably later in composition as well; they consist of the following parts:
1. Kyrie – which is only part of the Roman rite that has remained in the Greek language and is litanic invocation for mercy.
2. Gloria – the Gloria is a hymn of praise to the Holy Trinity, and occurs at Masses of a certain rank, currently on Sundays and the days with the rank of feast or solemnity.
3. Credo – the symbol or Credo is a doctrinal compilation of the central tenets of our Catholic Faith as defined by the Church Councils.
4. Sanctus – A hymn of praise taken from the book of Isaiah.
5. Agnus Dei – a litanic prayer invoking the mercy of the Lord and asking for His peace.
6. Ite missa est – the Chant of dismissal to the congregation sung by the deacon at the end of Mass.
The Propers of the Mass are texts set to music the accompany the various liturgical actions of the rite and as such consist of:
1. Introit – The Introit is the antiphon that is sung as the priest and the ministers enter the church at the beginning of Mass. It originally consisted of the psalm sung by the choir and/or congregation as the ministers approach the altar. The text of this antiphon generally comes from the psalms or some other part of sacred scripture, although they can sometimes be other texts. The structure of the Introit is ABA: the antiphon is sung in its entirety; a verse from psalms is sung on a recitation tone after; the doxology (“Glory be to the Father and to the Son and to the Holy Spirit…”) is sung and the antiphon is repeated. In general the style of the introits is sober and conducive to congregational singing.
2. Gradual – the Gradual takes its name from the steps of the ambo, because this was the chant sung as the deacon approached the ambo to chant the Gospel for the day. Graduals are often florid and virtuosic in their style and are generally sung by a smaller group or schola of more experienced singers.
3. Alleluia – the Alleluia is sung immediately before the Gospel is chanted or proclaimed. It consists of a florid singing of the word Alleluia – which is an expression of highest joy and triumph, praising the Lord. This is followed with a verse with a text from scripture or another source also in a melismatic style, after which the word Alleluia is repeated.
4. Offertory – the Offertory antiphon is sung during the preparation and offering of the gifts prior to the preface, Sanctus and Eurharistic prayer.
5. Communion – The Communion antiphon is sung after the priest’s communion.
The treatment of the proper chants of the Mass does not take into account the Sequence – a chant that follows the Alleluia immediately before the Gospel. Before the Council of Trent (1645 – 1663) Sequences were common and highly localized – each regional church might have its own repertoire of chants. Trent purged (for good or for ill) all but four of these Sequences: Victimae paschal laudes for Easter; Veni Sancte Spiritus for Pentecost; Lauda Sion Salvatorem for Corpus Christi and the Dies Irae for All Souls and Masses for the dead. In the 18th century, the Stabat Mater for Our Lady of Sorrows (September 15) was added to the list. The Norbertine books (like the Dominicans) also counted a sequence Laetabundus (Not in the Roman Missal) for Christmas.
The complex repertory consists of a rich latering of texts and melodies from different times and different books of the Scriptures and is one of the most precious parts of the treasury of the Church – sacred sounds of word and tone that have resonated the air down through the centuries and will continue to do so until the day of the Lord Jesus.