20 Let us therefore persuade it to make this first change for the better, by the avoidance of oaths; for although I spoke to you yesterday, and the day before, on this same subject; yet neither today, nor tomorrow, nor the day after, will I desist giving my counsel on this subject. And why do I say tomorrow and the day following? Until I see that you are amended, I will not abstain from doing so. If those, indeed, who transgress this law, are not ashamed, far less should we who bid them not transgress it, feel this frequency of the admonition to be a matter worthy of shame.
For to be continually reminding men of the same topics is not the fault of the speaker, but of the hearers, needing as they do perpetual instruction, upon simple and easily-observed precepts. What indeed is easier than not to swear? It is only a good work of habit. It is neither labour of the body, nor expenditure of wealth. Are you desirous to learn how it is possible to get the better of this infirmity, how it is possible to be set free from this evil habit? I will tell you of a particular method by which if pursued you will certainly master it.
If you see either yourself or any other person, whether it be one of your servants, or of your children, or your wife, ensnared in this vice; when you have continually reminded them of it, and they are not amended, order them to retire to rest supperless; and impose this sentence upon yourself, as well as upon them, a sentence which will bring with it no injury, but a gain. For such is the nature of spiritual acts; they bring profit and a speedy reformation. The tongue when constantly punished, when straitened by thirst. and pained by hunger, receives a sufficient admonition, even while no one is its monitor; and though we were the most stupid of mortals, yet when we are thus reminded by the greatness of the punishment during a whole day, we shall need no other counsel and exhortation.
Source: Homilies on the Statues (New Advent)