Confession, in Roman Catholic theology, means a declaration of sins to a priest in order to obtain absolution. The word, however, has borne very different meanings at different times, and the changes in sense mark important stages in the development of discipline and doctrine. St James (v. 16) speaks of that spontaneous confession which Christians make 'one to another' out of humility and brotherly love; and, much in the same spirit, Origen (Hom. in Ps. xxxvii.) recommends the sinner to seek out a physician 'learned and merciful,' to whom he may disclose his wounds, and from whom he may get advice. In all this there is no question of strict obligation on the one hand, or of priestly power upon the other. Still, even before Origen's time, the word had acquired a new significance. From the close of the 2d century at latest the church marked out for special reprobation those sins which were called 'mortal'—viz. murder, idolatry, and adultery. The guilty person was required to make public confession, he was subjected to penitential exercises, and was either excluded during life from the communion of the church, or readmitted, after long discipline, by the bishop, who imposed his hands upon him. The list of 'mortal offences' was extended during the 5th and the following centuries to all crimes which the Roman law punished with death, exile, or grave corporal penalty, and Leo I. (440-461 A.D.), in a famous letter to the Bishops of Apulia (Ep. 168), substituted private confession to the priest for public confession to the congregation. But the essential points of difference between ancient and modern or sacramental confession remained. In the former, the church only required confession to man of certain enormous offences, and left the mass of sins which are now called mortal to the judgment of God; and she exercised the power of 'binding and loosing' by excluding sinners from, and readmitting them to, her communion. Such power is really inherent in every society, though of course the church claimed to hold it by divine commission (Matt. xvi. 19, xviii. 18; John, xx. 22, 23), and insisted on the serious consequences which it involved. We can trace the faint beginnings of the modern system in the practice which prevailed in monasteries and nunneries of confessing breaches of the rule to the superiors (Jerome, De Reg. Monachorum; Basil, Reg. Brev.), and in the growing habit of seeking advice from priests by secret confession. The thirty-third canon of the Council of Châlons, which was held 813 A.D., throws great light on the state of things then existing. Some, the council says, maintain that 'sins should be confessed to God alone,' others to God and to the priest. The council finds no fault with either view, and remarks that confession to God purges the conscience from sin, while confession to the priest teaches the penitent 'how his sins are to be purged.' Even Peter Lombard, the great theological authority of the 12th century (In Sentent. lib. iv.), occupies the same ground as the Council of Châlons; and Aquinas (Supplement to the Summa) admits that in Lombard's time the necessity of confessing all mortal sins to the priest was an open question. Meantime, the fourth Lateran Council in 1215 (can. xxi.) had required all the faithful who have come to the years of discretion to confess their sins at least once a year to their parish priest, or with his leave to another priest. The doctrine received its final form in the Council of Trent (Sess. xiv.). The council explains 'mortal sins' to mean all sins, 'even sins of thought' which separate the soul from God. It declares that for mortal sin after baptism, confession to an approved priest, in act if possible, in desire if a priest cannot be had, is by divine institution the one and only remedy. This confession must embrace every mortal sin which can be recalled after careful self-examination. Further, it declares that the secret confession of mortal sins has always been practised in the church, and whereas in Peter Lombard's time Roman Catholics were free to hold that absolution was no more than a declaration of forgiveness by God, the council condemns this opinion under anathema. But it is careful to add that confession and absolution, in order to avail, must be accompanied by sincere sorrow before God for sin past, and a firm purpose of amendment. By the present canon law, Roman Catholics living in the world may choose any priest approved by the bishop as their confessor. The confession of slight or venial sins remains a matter of counsel and not of precept.
Confession to a priest is prescribed by the Greek and most of the Oriental churches, and the Church of England recommends private confession in the case of the sick, though it has never enforced the use of it. In 1873, 483 Anglican clergymen presented a petition to Convocation for the education, selection, and licensing of duly qualified confessors. That petition fell flat; but confession is regularly practised among a considerable section of the English communion. The Lutherans at first were inclined to retain some sort of private confession, but they were content with confession of a general kind, and have allowed it to fall into disuse. It is entirely rejected by Presbyterians, Methodists, Congregationalists, Baptists, &c.
The 'seal of confession' is the obligation which binds the priest to make no use whatever outside of the confessional of the knowledge acquired there. It is imposed under severe penalties by the fourth Lateran Council. See CONFIDENTIALITY, and Lea's History of Auricular Confession (3 vols. 1896).