Objection 1. It would seem that fraternal correction is not a matter of precept. For nothing impossible is a matter of precept, according to the saying of Jerome [Pelagius, Expos. Symb. ad Damas]: "Accursed be he who says that God has commanded any. thing impossible." Now it is written (Ecclesiastes 7:14): "Consider the works of God, that no man can correct whom He hath despised." Therefore fraternal correction is not a matter of precept.
Objection 2. Further, all the precepts of the Divine Law are reduced to the precepts of the Decalogue. But fraternal correction does not come under any precept of the Decalogue. Therefore it is not a matter of precept.
Objection 3. Further, the omission of a Divine precept is a mortal sin, which has no place in a holy man. Yet holy and spiritual men are found to omit fraternal correction: since Augustine says (De Civ. Dei i, 9): "Not only those of low degree, but also those of high position, refrain from reproving others, moved by a guilty cupidity, not by the claims of charity." Therefore fraternal correction is not a matter of precept.
Objection 4. Further, whatever is a matter of precept is something due. If, therefore, fraternal correction is a matter of precept, it is due to our brethren that we correct them when they sin. Now when a man owes anyone a material due, such as the payment of a sum of money, he must not be content that his creditor come to him, but he should seek him out, that he may pay him his due. Hence we should have to go seeking for those who need correction, in order that we might correct them; which appears to be inconvenient, both on account of the great number of sinners, for whose correction one man could not suffice, and because religious would have to leave the cloister in order to reprove men, which would be unbecoming. Therefore fraternal correction is not a matter of precept.
On the contrary, Augustine says (De Verb. Dom. xvi, 4): "You become worse than the sinner if you fail to correct him." But this would not be so unless, by this neglect, one omitted to observe some precept. Therefore fraternal correction is a matter of precept.
I answer that, Fraternal correction is a matter of precept. We must observe, however, that while the negative precepts of the Law forbid sinful acts, the positive precepts inculcate acts of virtue. Now sinful acts are evil in themselves, and cannot become good, no matter how, or when, or where, they are done, because of their very nature they are connected with an evil end, as stated in Ethic. ii, 6: wherefore negative precepts bind always and for all times. On the other hand, acts of virtue must not be done anyhow, but by observing the due circumstances, which are requisite in order that an act be virtuous; namely, that it be done where, when, and how it ought to be done. And since the disposition of whatever is directed to the end depends on the formal aspect of the end, the chief of these circumstances of a virtuous act is this aspect of the end, which in this case is the good of virtue. If therefore such a circumstance be omitted from a virtuous act, as entirely takes away the good of virtue, such an act is contrary to a precept. If, however, the circumstance omitted from a virtuous act be such as not to destroy the virtue altogether, though it does not perfectly attain the good of virtue, it is not against a precept. Hence the Philosopher (Ethic. ii, 9) says that if we depart but little from the mean, it is not contrary to the virtue, whereas if we depart much from the mean virtue is destroyed in its act. Now fraternal correction is directed to a brother's amendment: so that it is a matter of precept, in so far as it is necessary for that end, but not so as we have to correct our erring brother at all places and times.
Reply to Objection 1. In all good deeds man's action is not efficacious without the Divine assistance: and yet man must do what is in his power. Hence Augustine says (De Correp. et Gratia xv): "Since we ignore who is predestined and who is not, charity should so guide our feelings, that we wish all to be saved." Consequently we ought to do our brethren the kindness of correcting them, with the hope of God's help.
Reply to Objection 2. As stated above (32, 5, ad 4), all the precepts about rendering service to our neighbor are reduced to the precept about the honor due to parents.
Reply to Objection 3. Fraternal correction may be omitted in three ways.
First, meritoriously, when out of charity one omits to correct someone. For Augustine says (De Civ. Dei i, 9): "If a man refrains from chiding and reproving wrongdoers, because he awaits a suitable time for so doing, or because he fears lest, if he does so, they may become worse, or hinder, oppress, or turn away from the faith, others who are weak and need to be instructed in a life of goodness and virtue, this does not seem to result from covetousness, but to be counselled by charity."
Secondly, fraternal correction may be omitted in such a way that one commits a mortal sin, namely, "when" (as he says in the same passage) "one fears what people may think, or lest one may suffer grievous pain or death; provided, however, that the mind is so dominated by such things, that it gives them the preference to fraternal charity." This would seem to be the case when a man reckons that he might probably withdraw some wrongdoer from sin, and yet omits to do so, through fear or covetousness.
Thirdly, such an omission is a venial sin, when through fear or covetousness, a man is loth to correct his brother's faults, and yet not to such a degree, that if he saw clearly that he could withdraw him from sin, he would still forbear from so doing, through fear or covetousness, because in his own mind he prefers fraternal charity to these things. It is in this way that holy men sometimes omit to correct wrongdoers.
Reply to Objection 4. We are bound to pay that which is due to some fixed and certain person, whether it be a material or a spiritual good, without waiting for him to come to us, but by taking proper steps to find him. Wherefore just as he that owes money to a creditor should seek him, when the time comes, so as to pay him what he owes, so he that has spiritual charge of some person is bound to seek him out, in order to reprove him for a sin. On the other hand, we are not bound to seek someone on whom to bestow such favors as are due, not to any certain person, but to all our neighbors in general, whether those favors be material or spiritual goods, but it suffices that we bestow them when the opportunity occurs; because, as Augustine says (De Doctr. Christ. i, 28), we must look upon this as a matter of chance. For this reason he says (De Verb. Dom. xvi, 1) that "Our Lord warns us not to be listless in regard of one another's sins: not indeed by being on the lookout for something to denounce, but by correcting what we see": else we should become spies on the lives of others, which is against the saying of Proverbs 24:19: "Lie not in wait, nor seek after wickedness in the house of the just, nor spoil his rest." It is evident from this that there is no need for religious to leave their cloister in order to rebuke evil-doers.
Source: Summa Theologica (New Advent)