The custom of swearing must be resisted more diligently.
But it is the custom, it is usually said. It is usually said when I do not say. This is: Above all. What is: Above all? Be wary before others, more intent on this than on other matters. Greater custom demands greater intent, not the custom of something trivial. If you were doing something with your hand, it would be easier to command your hand not to do it; if you had to walk somewhere with your feet, with laziness holding you back, you would stir yourself to get up and go. The tongue has the ease of movement, being placed in a slick environment, it easily slips on the slippery. The faster and easier it moves, the more you should be steadfast against it. You will subdue it if you stay alert; you will stay alert if you fear; you will fear if you consider yourself to be a Christian. For swearing has so much evil that those who worship stones fear to swear falsely by stones; do you not fear the present God, the living God, the knowing God, the remaining God, the God avenging the contemptible? He closes the temple over a stone and goes to his home; he himself has shut up over his god, and yet when it is said to him: Swear by Jupiter, he fears the eyes of the present.
To swear falsely by idols is perjury.
And behold, I say to your Charity, that even he who swears by a false stone is perjured. Why do I say this? Because many are deceived in this matter, and think that since it is nothing by which they swear, they are not held in the crime of perjury. You are certainly perjured because you swear falsely by that which you consider sacred. But I do not consider it sacred. It is considered sacred by the one to whom you swear. For when you swear, you do not swear to yourself, nor to the stone; but you swear to your neighbor. You swear to a man before a stone; but is it not also before God? The stone does not hear you speaking; but God punishes you for deceiving.
How the custom of swearing an oath is overturned.
Above all, therefore, my brothers, I beseech you, that God has compelled me to speak these things not without cause. For I say before Him what I have said, often I have avoided this question; I feared that by warning and advising I would make more guilty those who would not listen; however, today I feared more that I would refuse to speak, when I was commanded to speak. As though the fruit of this labor of mine is small, if all who have applauded me also cry out against themselves, so that they may not falsely swear against themselves; if so many people who have listened to me very attentively be attentive against their own custom, and remind themselves today, when they have come to their homes, when by a slip of the tongue they repeat their habit; let each neighbor remind the other: This is what we heard today, this is what we are bound to. Let it not be done today, certainly while the speech is fresh: I speak from experience; let it not be done today, it is more sluggish to accomplish tomorrow. If it is not done even tomorrow, the one who keeps watch labors less; for he is aided by the custom of the previous day. In three days the plague from which we suffer dies; and we will rejoice in your fruit; because you will abound with great good, if you will be free from such a great evil. Turned to the Lord, etc.