The following is taken from the Introduction to the Devout Life. This is especially relevant to persons who are inclined to scrupulosity and discouragement.
One important direction in which to exercise gentleness, is with respect to ourselves, never growing irritated with one's self or one's imperfections; for although it is but reasonable that we should be displeased and grieved at our own faults, yet ought we to guard against a bitter, angry, or peevish feeling about them.
Many people fall into the error of being angry because they have been angry, vexed because they have given way to vexation, thus keeping up a chronic state of irritation, which adds to the evil of what is past, and prepares the way for a fresh fall on the first occasion. Moreover, all this anger and irritation against one's self fosters pride, and springs entirely from self-love, which is disturbed and fretted by its own imperfection.
What we want is a quiet, steady, firm displeasure at our own faults. A judge gives sentence more effectually speaking deliberately and calmly than if he be impetuous and passionate (for in the latter case he punishes not so much the actual faults before him, but what they appear to him to be); and so we can chasten ourselves far better by a quiet stedfast repentance, than by eager hasty ways of penitence, which, in fact, are proportioned not by the weight of our faults, but according to our feelings and inclinations.
Thus one man who specially aims at purity will be intensely vexed with himself at some very trifling fault against it, while he looks upon some gross slander of which he has been guilty as a mere laughing matter.
On the other hand, another will torment himself painfully over some slight exaggeration, while he altogether overlooks some serious offence against purity; and so on with other things. All this arises solely because men do not judge themselves by the light of reason, but under the influence of passion.
Believe me, my daughter, as a parent's tender affectionate remonstrance has far more weight with his child than anger and sternness, so, when we judge our own heart guilty, if we treat it gently, rather in a spirit of pity than anger, encouraging it to amendment, its repentance will be much deeper and more lasting than if stirred up in vehemence and wrath.
For instance:--Let me suppose that I am specially seeking to conquer vanity, and yet that I have fallen conspicuously into that sin;--instead of taking myself to task as abominable and wretched, for breaking so many resolutions, calling myself unfit to lift up my eyes to Heaven, as disloyal, faithless, and the like, I would deal pitifully and quietly with myself. "Poor heart! so soon fallen again into the snare! Well now, rise up again bravely and fall no more. Seek God's Mercy, hope in Him, ask Him to keep you from falling again, and begin to tread the pathway of humility afresh. We must be more on our guard henceforth." Such a course will be the surest way to making a steadfast substantial resolution against the special fault, to which should be added any external means suitable, and the advice of one's director.
If any one does not find this gentle dealing sufficient, let him use sterner self-rebuke and admonition, provided only, that whatever indignation he may rouse against himself, he finally works it all up to a tender loving trust in God, treading in the footsteps of that great penitent who cried out to his troubled soul: "Why art thou so vexed, O my soul, and why art thou so disquieted within me? O put thy trust in God, for I will yet thank Him, Which is the help of my countenance, and my God." (Ps. xlii. 11, 15.)
So then, when you have fallen, lift up your heart in quietness, humbling yourself deeply before God by reason of your frailty, without marvelling that you fell;--there is no cause to marvel because weakness is weak, or infirmity infirm. Heartily lament that you should have offended God, and begin anew to cultivate the lacking grace, with a very deep trust in His Mercy, and with a bold, brave heart.