Theory and practice of the confessional by Caspar Erich Schieler, Richard Frederick Clarke
3. Necessity of the Sacrament of Penance.
The Council of Trent declared in its fourteenth session, with regard to this point: "The Sacrament of Penance is as necessary to those who have incurred mortal sin after baptism, as baptism itself is to those who are not yet regenerated." (Trid. Sess. XIV. ep. 2.) It follows from this teaching of the Council that, since Baptism is indispensable to eternal salvation, penance is equally necessary. To use the exact language of theologians, it is necessary in re vel saltern in voto. Which means that those who can actually receive the Sacrament are bound to have recourse to it in order to be freed from their sins; but that those for whom the reception of this Sacrament is for any reason impossible, will be cleansed from their sins by the desire of receiving it. This desire is always included in perfect contrition. (Cf. S. Th. Quodl. I. a. 12; S. Alph. Theol. Mor. Lib. VII. n. 600 Lehmkuhl, 1. c. n. 255; Müller, 1. c. Sect. 107, in fine.)
For when Our Lord granted to His apostles the power of forgiving or retaining sins, and thereby instituted the Sacrament of Penance for the remission of grievous sin, committed after Baptism, He evidently asserted it to be His will that the sinner should be subjected to the power of the keys by the reception of this Sacrament, the latter thus becoming a necessary means of obtaining pardon for grievous sin committed after baptismal regeneration. The power of the keys vested in the apostles and their successors would be a useless gift if the faithful, without submitting to that power, could be released from their sins and gain the heavenly kingdom. The more so, as the priest possesses also the power of retaining sins; a power unfavorable to the sinner; but which the sinner could elude if the Sacrament of Penance had not been made a necessary means of forgiveness. Nor would the sinner undergo the inconveniences connected with the reception of the Sacrament of Penance, if he were not persuaded of Christ's precept, imposing the Sacrament of Penance as a means of reconciliation. Venial sins, however, are forgiven without reference to the Sacrament of Penance, as we shall show in another place.
Thus, by divine precept, all who have incurred mortal sin after Baptism are bound to receive this Sacrament. The obligation is absolute (per se) in danger of death; for, in this case, the reception is necessary. Hence those are bound who are suffering of a dangerous disease; a mother before her first confinement, or before any subsequent birth, if her travails are of an especially alarming nature; a criminal sentenced to death, before his execution; and any one foreseeing the lack of another opportunity for his whole life of making a confession.
There are other times in the course of our life when the obligation of confession becomes actual and pressing; the Church, acting according to the intentions of Christ, has specified these occasions more particularly. For the Sacrament was not instituted merely to dispose man for his passage from this life, but also to heal his spiritual infirmities, to shield him against relapse into sin, and to strengthen him to lead a virtuous life. Consequently, we would frustrate the object of the Sacrament if we were to postpone its reception to the hour of death.
Per accidens it is obligatory to receive this Sacrament: (1) for a person who desires or is bound to receive holy Communion, and who happens to be in a state of mortal sin; (2) when the Sacrament of Penance is the only means for overcoming a temptation or avoiding grievous sin; (3) when any one feels himself incapable of making an act of perfect contrition, and yet is by his duties required to be in a state of grace; for instance, if one has to administer a Sacrament, or simply because one realizes that it is wrong to remain in a state of enmity with God for any considerable period." (S. Alph. Lib. VI. nn. 662, 665; Gury-Ball. II. n. 466; Ballerini. Ant. S. J. Opus Theol. Mor. Vol. V.; Tract, X. Sect. V. De Sacram. Pœn. cp. III. n. 1025 88.; Aertnys, Theol. Mor. Lib. VI. n. 229.)