Cheating and dishonest ways of making money are utterly unfit for clerics whose duty is to serve all. They ought never to be involved in a money affair, unless it is one affecting a man's life. For them the example of David is given, that they should injure none, even when provoked; also the death of Naboth, to keep them from preferring life to virtue.
57. Nothing is more odious than for a man to have no love for a virtuous life, but instead to be kept excited by an unworthy business in following out a low line of trade, or to be inflamed by an avaricious heart, and by day and by night to be eager to damage another's property, not to raise the soul to the splendour of a virtuous life, and not to regard the beauty of true praise.
58. Hence rise inheritances sought by cunning words and gained under pretence of being self-restrained and serious. But this is absolutely abhorrent to the idea of a Christian man. For everything gained by craft and got together by cheating loses the merit of openness. Even among those who have undertaken no duty in the ranks of the clergy it is considered unfitting to seek for the inheritance of another. Let those who are reaching the end of their life use their own judgment, so that they may freely make their wills as they think best, since they will not be able to amend them later. For it is not honourable to divert the savings that belong to others or have been got together for them. It is further the duty of the priest or the cleric to be of use if possible to all and to be harmful to none.
59. If it is not possible to help one without injuring another, it is better to help neither than to press hard upon one. Therefore it is not a priest's duty to interfere in money affairs. For here it must often happen that he who loses his case receives harm; and then he considers that he has been worsted through the action of the intervener. It is a priest's duty to hurt no one, to be ready to help all. To be able to do this is in God's power alone. In a case of life and death, without doubt it is a grave sin to injure him whom one ought to help when in danger. But it is foolish to gain others' hate in taking up money matters, though for the sake of a man's safety great trouble and toil may often be undertaken. It is glorious in such a case to run risks. Let, then, this be firmly held to in the priestly duties, namely, to injure none, not even when provoked and embittered by some injury. Good was the man who said: “If I have rewarded evil to those who did me good.” For what glory is it if we do not injure him who has not injured us? But it is true virtue to forgive when injured.
60. What a virtuous action was that, when David wished rather to spare the king his enemy, though he could have injured him! How useful, too, it was, for it helped him when he succeeded to the throne. For all learned to observe faith to their king and not to seize the kingdom, but to fear and reverence him. Thus what is virtuous was preferred to what was useful, and then usefulness followed on what was virtuous.
61. But that he spared him was a small matter; he also grieved for him when slain in war, and mourned for him with tears, saying: You mountains of Gilboa, let neither dew nor rain fall upon you; ye mountains of death, for there the shield of the mighty is cast away, the shield of Saul. It is not anointed with oil, but with the blood of the wounded and the fat of the warriors. The bow of Jonathan turned not back and the sword of Saul returned not empty. Saul and Jonathan were lovely and very dear, inseparable in life, and in death they were not divided. They were swifter than eagles, they were stronger than lions. You daughters of Israel, weep over Saul, who clothed you in scarlet with your ornaments, who put on gold upon your apparel. How are the mighty fallen in the midst of the battle! Jonathan was wounded even to death. I am distressed for you, my brother Jonathan; very pleasant have you been unto me. Your love came to me like the love of women. How have the mighty fallen and the longed-for weapons perished!
62. What mother could weep thus for her only son as he wept here for his enemy? Who could follow his benefactor with such praise as that with which he followed the man who plotted against his life? How affectionately he grieved, with what deep feeling he bewailed him! The mountains dried up at the prophet's curse, and a divine power filled the judgment of him who spoke it. Therefore the elements themselves paid the penalty for witnessing the king's death.
63. And what, in the case of holy Naboth, was the cause of his death, except his regard for a virtuous life? For when the king demanded the vineyard from him, promising to give him money, he refused the price for his father's heritage as unseemly, and preferred to shun such shame by dying. “The Lord forbid it me, that I should give the inheritance of my fathers unto you;” that is, that such reproach may not fall on me, that God may not allow such wickedness to be attained by force. He is not speaking about the vines— nor has God care for vines or plots of ground— but he says it of his fathers' rights. He could have received another or the king's vineyards and been his friend, wherein men think there is no small usefulness so far as this world is concerned. But because it was base he thought it could not be useful, and so he preferred to endure danger with honour intact, rather than gain what was useful to his own disgrace. I am here again speaking of what is commonly understood as useful, not that in which there is the grace of virtuous life.
64. The king could himself have taken it by force, but that he thought too shameless; then when Naboth was dead he grieved. The Lord also declared that the woman's cruelty should be punished by a fitting penalty, because she was unmindful of virtue and preferred a shameful gain.
65. Every kind of unfair action is shameful. Even in common things, false weights and unjust measures are accursed. And if fraud in the market or in business is punished, can it seem free from reproach if found in the midst of the performance of the duties of virtue? Solomon says: “A great and a little weight and various measures are an abomination before the Lord.” Before that it also says: “A false balance is abomination to the Lord, but a just weight is acceptable to Him.”
Source: On the Duties of the Clergy (New Advent)