This, like many other prayers of the Church, receives its name from the Latin word with which it begins, Confiteor, I confess. It is a general avowal of sins, in the presence of God, of the Church Triumphant in heaven and of the Church Militant on earth. The reciter thrice strikes his breast, in acknowledgment of the three kinds of sins of which he has been guilty,—of thought, of word and of deed,—and concludes by begging the intercession of the Blessed Virgin, of the Saints and of his brethren on earth.
The Confiteor is one of the Liturgical prayers, and hence a Sacramental. It is said by the celebrant and assistant ministers at Mass, in that part of the Divine Office called Compline, and sometimes, also, at Prime. The learned and pious Cardinal Bona says, in his book de Rebus Liturgicis, that some writers have attributed the authorship of this prayer to Pope St. Pontianus, others to Pope St. Damasus. The former Pontiff reigned from 230 to 235; the latter from 366 to 384. “I am convinced,” continues His Eminence, “that some general formula of confession was in use from Apostolic times, but I am unable to decide whether the one we now have originated with Pontianus or Damasus, because ancient writers say nothing of the matter.”
The priests and prophets of the Old Law made a general confession of their sins before praying or offering sacrifice: peccavimus, Domine, injuste egimus, iniquitatem fecimus—we have sinned, O Lord, we have acted unjustly, we have done Iniquity. All the ancient Liturgies contain a Confiteor, different in words, but not in sentiments, from the one now in use. An abiding sorrow for sin and confession of it are essential elements of Christian holiness; no system of worship is sound which does not, at least implicitly, contain them. The practice of striking the breast, in token of repentance, is based on natural reason, Scripture and tradition. The heart, the seat of the passions both good and bad, is in the breast. When the intellect sins by pride or curiosity, it but follows the promptings of the heart. It is right then that we should strike the breast rather than any other part of the body. By doing so, we show that we wish to rend our hearts, that our contrition is not of the lip but of the heart. The humble publican who went down to his house justified rather than the proud Pharisee struck his breast when he prayed, O God be merciful to me a sinner (St. Luke, xviii. 13.) Those who witnessed the prodigies which followed the death of Christ on Calvary returned home, striking their breasts. St. Gregory Nazianzen, a Father of the 4th century, says (Orat. 15): “Let us, clothed with sackcloth, enter the temple, and day and night strike our breasts between the steps and the altar.” St. Augustine bears testimony to the existence of the same practice in his time.