Confiteor

The Confiteor (so named from its first word, or incipit, in Latin, meaning "I confess" or "I acknowledge") is one of the prayers that can be said during the Penitential Act at the beginning of Mass of the Roman Rite in the Catholic Church. It is also said in the Lutheran Church at the beginning of the Divine Service, and by some Anglo-catholic Anglicans before Mass. The prayer is started by the Priest and ended by the people.

While the original Eastern liturgies begin with a confession of sin made by the celebrant, the earliest records of the Roman Rite all describe the Mass as beginning at the Introit, but the celebrant may have used a Confiteor-like confession of sinfulness as one of the private prayers he said in the sacristy before he began Mass. Only in the 10th or 11th century is there any evidence of the preparation being made at the altar.

Outside of Mass some prayers similar to the Confiteor appear earlier. The "Canonical Rule" of Chrodegang of Metz (d. 743) recommends: "First of all prostrate yourself humbly in the sight of God ... and pray Blessed Mary with the holy Apostles and Martyrs and Confessors to pray to the Lord for you." And Egbert of York (d. 766) gives a short form that is the germ of our present prayer: "Say to him to whom you wish to confess your sins: through my fault that I have sinned exceedingly in thought, word, and deed." In answer the confessor says almost exactly the Misereatur.

The Confiteor is first found quoted as part of the introduction of the Mass in Bernold of Constance (d. 1100). The Misereatur and Indulgentiam follow, the former slightly different, but the latter exactly as it was in the Tridentine Missal. The Tridentine form of the Confiteor is found in the 14th-century "Ordo Romanus XIV" with only a slight modification, and is found word for word in a decree of the Third Council of Ravenna (1314).

The form, and especially the list of saints invoked, varied considerably in the Middle Ages. The Carthusian, Carmelite, and Dominican Offices, whose Missals, having existed for more than 200 years before 1570, were still allowed, had forms of Confiteor that differed from that in the Tridentine Missal. These three forms were quite short, and contained only one "mea culpa"; the Dominicans invoked, besides the Blessed Virgin, St. Dominic. Moreover, some other orders had the privilege of adding the name of their founder after that of St. Paul. The Franciscans for instance, inserted the name of St. Francis, and many Benedictine houses added the name of their founder, St. Benedict. The local patron was inserted at the same place in a few local uses.

...
Wikipedia