Chapter 19 — Part II: The Sacraments — Penance
Section 23. Why Christ Instituted This Sacrament — In the first place, however, it will be well to explain why it is that Christ our Lord was pleased to number Penance among the Sacraments. One of His reasons certainly was to leave us no room for doubt regarding the remission of sin which was promised by God when He said: If the wicked do penance, etc. For each one has good reason to distrust the accuracy of his own judgment on his own actions, and hence we could not but be very much in doubt regarding the truth of our internal penance. It was to destroy this, our uneasiness, that our Lord instituted the Sacrament of Penance, by means of which we are assured that our sins are pardoned by the absolution of the priest; and also to tranquilize our conscience by means of the trust we rightly repose in the virtue of the Sacraments. The words of the priest sacramentally and lawfully absolving us from our sins are to be accepted in the same sense as the words of Christ our Lord when He said to the paralytic: Son, be of good heart: thy sins are forgiven thee.