I don’t know if his teaching on this subject is still acceptable but St. Thomas Aquinas talks quite a bit about
Penance in his
Summa Theologica and in the
Supplement to the Third Part.
For instance, St. Thomas Aquinas discusses this in
Summa Theologica (III, 86, 4):
Whether the debt of punishment remains after the guilt has been forgiven through Penance?
…
Reply to Objection 3. Christ’s Passion is of itself sufficient to remove all debt of punishment, not only eternal, but also temporal; and man is released from the debt of punishment according to the measure of his share in the power of Christ’s Passion. Now in Baptism man shares the Power of Christ’s Passion fully, since by water and the Spirit of Christ, he dies with Him to sin, and is born again in Him to a new life, so that, in Baptism, man receives the remission of all debt of punishment. In Penance, on the other hand, man shares in the power of Christ’s Passion according to the measure of his own acts, which are the matter of Penance, as water is of Baptism, as stated above (84, 1,3). Wherefore the entire debt of punishment is not remitted at once after the first act of Penance, by which act the guilt is remitted, but only when all the acts of Penance have been completed.
A related topic is discussed, for instance, in
Supplement to the Third Part( 5, 2) of St. Thomas Aquinas’ Summa Theologica:Whether contrition can take away the debt of punishment entirely?
**.…**
I answer that, The intensity of contrition may be regarded in two ways. First, on the part of charity, which causes the displeasure, and in this way it may happen that the act of charity is so intense that the contrition resulting therefrom merits not only the removal of guilt, but also the remission of all punishment. Secondly, on the part of the sensible sorrow, which the will excites in contrition: and since this sorrow is also a kind of punishment, it may be so intense as to suffice for the remission of both guilt and punishment.
Reply to Objection 1. A man cannot be sure that his contrition suffices for the remission of both punishment and guilt: wherefore he is bound to confess and to make satisfaction, especially since his contrition would not be true contrition, unless he had the purpose of confessing united thereto: which purpose must also be carried into effect, on account of the precept given concerning confession.