One of the duties of fortitude is to keep the weak from receiving injury; another, to check the wrong motions of our own souls; a third, both to disregard humiliations, and to do what is right with an even mind. All these clearly ought to be fulfilled by all Christians, and especially by the clergy.
179. The glory of fortitude, therefore, does not rest only on the strength of one's body or of one's arms, but rather on the courage of the mind. Nor is the law of courage exercised in causing, but in driving away all harm. He who does not keep harm off a friend, if he can, is as much in fault as he who causes it. Wherefore holy Moses gave this as a first proof of his fortitude in war. For when he saw an Hebrew receiving hard treatment at the hands of an Egyptian, he defended him, and laid low the Egyptian and hid him in the sand. Solomon also says: “Deliver him that is led to death.”
180. From whence, then, Cicero and Panætius, or even Aristotle, got these ideas is perfectly clear. For though living before these two, Job had said: “I delivered the poor out of the hand of the strong, and I aided the fatherless for whom there was no helper. Let the blessing of him that was ready to perish come upon me.” Was not he most brave in that he bore so nobly the attacks of the devil, and overcame him with the powers of his mind? Nor have we cause to doubt the fortitude of him to whom the Lord said: “Gird up your loins like a man. Put on loftiness and power. Humble every one that does wrong.” The Apostle also says: “You have a strong consolation.” He, then, is brave who finds consolation in any grief.
181. And in very truth, rightly is that called fortitude, when a man conquers himself, restrains his anger, yields and gives way to no allurements, is not put out by misfortunes, nor gets elated by good success, and does not get carried away by every varying change as by some chance wind. But what is more noble and splendid than to train the mind, keep down the flesh, and reduce it to subjection, so that it may obey commands, listen to reason, and in undergoing labours readily carry out the intention and wish of the mind?
182. This, then, is the first notion of fortitude. For fortitude of the mind can be regarded in two ways. First, as it counts all externals as very unimportant, and looks on them as rather superfluous and to be despised than to be sought after. Secondly, as it strives after those things which are the highest, and all things in which one can see anything moral (or as the Greeks call it, πρέπον,) with all the powers of the mind. For what can be more noble than to train your mind so as not to place a high value on riches and pleasures and honours, nor to waste all your care on these? When your mind is thus disposed, you must consider how all that is virtuous and seemly must be placed before everything else; and you must so fix your mind upon that, that if anything happens which may break your spirit, whether loss of property, or the reception of fewer honours, or the disparagement of unbelievers, you may not feel it, as though thou were above such things; nay, so that even dangers which menace your safety, if undertaken at the call of justice, may not trouble you.
183. This is the true fortitude which Christ's warrior has, who receives not the crown unless he strives lawfully. Or does that call to fortitude seem to you but a poor one: “Tribulation works patience, and patience, experience, and experience, hope”? See how many a contest there is, yet but one crown! That call none gives, but he who was strengthened in Christ Jesus, and whose flesh had no rest. Affliction on all sides, fighting without and fears within. And though in dangers, in countless labours, in prisons, in deaths — he was not broken in spirit, but fought so as to become more powerful through his infirmities.
184. Think, then, how he teaches those who enter upon their duties in the Church, that they ought to have contempt for all earthly things: “If, then, you be dead with Christ from the elements of this world, why do ye act as though living in the world? Touch not, taste not, handle not, which all are to perish with the using.” And further: “If you then be risen with Christ, seek those things which are above, not those things which are on the earth.” And again: “Mortify, therefore, your members which are on the earth.” This, indeed, is meant for all the faithful. But you, especially, my son, he urges to despise riches and to avoid profane and old wives fables— allowing nothing but this: “Exercise yourself unto godliness, for bodily exercise profits a little, but godliness is profitable unto all things.”
185. Let, then, godliness exercise you unto justice, continence, gentleness, that you may avoid childish acts, and that rooted and grounded in grace you may fight the good fight of faith. Entangle not yourself in the affairs of this life, for you are fighting for God. For if he who fights for the emperor is forbidden by human laws to enter upon lawsuits, to do any legal business, or to sell merchandise; how much more ought he who enters upon the warfare of faith to keep from every kind of business, being satisfied with the produce of his own little bit of land, if he has it? If he has not that, let him be content with the pay he will get for his service. Here is a good witness to this fact, who says: “I have been young and now am old, yet have I not seen the righteous forsaken, nor his seed begging bread.” That is the true rest and temperance of the mind which is not excited by the desire of gain, nor tormented by the fear of want.
Source: On the Duties of the Clergy (New Advent)