Cardinal Manning mentions that a fourth effect of sins of omission is despondency.
“A consciousness of sin has the effect of depressing the soul, and, unless it soften it, of making it to doubt its own salvation; for where the charity of God and our neighbour has become low and faint, if it be not altogether lost, there both hope and faith begin likewise to decline. Any man who is conscious of his own sins, knows that though men do not see them or suspect them—though they are only half known and half seen even by his own conscience—they are all perfectly seen and known to the eye of Almighty God. This consciousness of sinfulness coupled with the consciousness of impenitence, the sense that he is not softened, nor humbled, but rather that he is irritated by the clear sight of his own sin and of the graces of those that are about him, lights up a high fever of resentful heat which grows more fierce as charity declines.”
“The will in its stiffness refuses to bow itself before God, and though a cloud on the conscience half hides many sins that are not altogether forgotten, he is half conscious of many and therefore full of fear. . . . A soul in that state becomes desponding and reckless, so that in a multitude of cases, instead of turning towards God by repentance, it turns recklessly away from God and plunges further into sin. . . . The moment hope is lost and the last spring is broken, a man who began only with sins of omission and then sins of sloth, will at last plunge recklessly into sins he never committed before, saying: ‘It is too late—I have gone too far—I am too bad.'”
“So long as there is a hope of salvation, a hope of pardon, and so long as a good name and fame among men is not lost, a man is sustained by a certain lingering confidence and restrained from a multitude of sins.” Peter denied Christ, but still loved Him, and never lost hope; he “went out and wept bitterly, and was forgiven.”
Quotations from Henry Edward Manning, Sin and Its Consequences, 2d ed. (London: Burns and Oates, 1874).