The mass is the latin liturgical rite that celebrates the Eucharist: the religious ritual that has been re-enacted for many centuries in the Roman Church. Until recent times, Roman mass celebrations were sung in latin (with a little Greek) using the liturgical text called the Ordinarium Missae (the ordinary of the mass).
The Ordinarium Missae is the consistent portion of the mass that is the same for each mass celebration. Another part of the mass called the Proprium Missae (the proper of the mass), on the other hand, consists of the text that is assigned to specific occasions.
Many different melodies were composed for the ancient Gregorian chant melodic repertory. However, beginning in the 13th century, composers began setting the words polyphonically, meaning that multiple melodies were sung at the same time as opposed to the singing of just a single melody: the case in Gregorian chant. Many different musical settings of the words of the ordinary have been composed over the centuries since then, and the mass text has been used as a basis of musical composition by the finest composers of the European tradition.
The ordinary of the mass has five parts:
1 – Kyrie: The first section of the ordinary of the mass is called the Kyrie. The phrase Kyrie eleison that is sung at the beginning is of Greek origin and became part of the Roman liturgy by the time of Gregory the Great (590-604). Sometime during the following 200 years, the phrase Christe eleison was added. In three parts, the traditional Kyrie movement consists of “kyrie eleison” sung three times, “Christe eleison” sung three times, then “Kyrie eleison” sung again three more times, usually using a different melody.
2 – Gloria: The text of the next section, the Gloria, took its position as a part of the ordinary by the 11th century. It’s text stems from the latin Gloria in excelsis Deo, or Glory to God in the highest.
3 - Credo: The Credo text contains the words of the Nicene creed, a dogmatic statement that was written by bishops during the early years of christianity and revised by the first council of Constantinople in 381AD. It became a part of the liturgy of the Eastern church during the following century and was adopted by the Roman catholic church in the 11th century.
4 – Sanctus: The original Sanctus text is from Isaiah 6:30 (holy, holy, holy, etc.) and from Matthew 21:9 (hosanna in excelsis). A Benedictus was then sung followed again by the text from Matthew 21:9. The text from Isaiah had entered the liturgy very early on. The Liber Pontificalis of 530 states that Sixtus II (119-128) proclaimed that it was to be sung as a communal prayer by the congregation. The hosanna and benedictus were added later on. The Sanctus may have remained a congregational chant until the 12th century.
5 - Agnus Dei: In the catholic liturgy, the singing of the Agnus Dei accompanied the breaking of the bread during the serving of the eucharist. It appears to have entered the mass in the late 7th century. The text is derived from John 1:29 and originally was repeated until the rite of the eucharist had completed. By the 12th century, however, the iterations were limited to three, with “grant us peace” (dona nobis pacem) substituted for “have mercy upon us.”