Theory and practice of the confessional by Caspar Erich Schieler, Richard Frederick Clarke
4. Forgiveness of Venial Sin.
(d) Contrition by itself also procures the remission of venial sins, and more especially when it is perfect (contritio), since, then, it destroys mortal sin and is, therefore, still more efficacious in the case of venial. Perfect contrition removes all venial sins if it is universal, that is to say if it extends to all venial sins, or if a man is disposed never more to commit venial sin and would be sorry for all his past sins, if they were present to his mind. On the other hand, an act of perfect contrition does not remit all venial sins, if it extends only to this or that particular venial sin, or if a person is disposed to avoid only one or other of his venial sins.
According to the teaching of the more numerous and distinguished theologians, even imperfect contrition remits venial sins; this imperfect contrition (attritio) must spring from some supernatural motive referring to God — such for instance as the thought that venial sin is a violation of the obedience or reverence due to God. By attritio the affection toward sin is entirely uprooted and the will is withdrawn from the sin, man turns again to God as his last end, and expiates his fault by his sorrow.
(e) Moreover, the "love of God above all things" remits venial sins if it is actual and formally or virtually opposed to venial sin.
(f) Lastly, venial sins are forgiven by good works done from a motive of penance (ex affectu pænitentiæ), especially those to which Holy Scripture assigns the virtue of destroying venial sin. Such are: prayer (John xiv. 13s.; xvi. 23), almsgiving and fasting, especially the works of mercy and mortification (Ecclus. iii. 33; iv. 1-11; Tob. iv. 11; Dan. iv. 24; Matt, v. 7; John iii. 5-10; 1 Reg. vii. 5, etc.; 1 Esdras viii. 21, etc.). Cf. S. Thom. II. II. Q. 147, art. 1 et 3.