Never to swear, but always to speak the truth, observe with equal zeal. For just as it is permitted to the carnal to swear for the terror of fraud, so oaths are forbidden to the spiritual, even when they are well aware in their own conscience. 'Let your speech,' He says, 'be Yea, yea; Nay, nay; for whatever is more than this comes of evil' (James 5). Beware therefore of swearing in a good cause, because it is of evil. And it is said to be of evil for this reason, that the necessity of swearing arises from an unbelieving conscience. For the necessity of swearing is extorted from that man whose faith remains in doubt. But you, who ought to show the simplicity of your heart with your lips, why do you bind yourself by a voluntary oath? Take away the practice of swearing in a good cause, and you will not forswear yourself in an evil one.
Speak the truth from the heart, and the necessity of swearing will be absent. For we read: 'Accustom not yourself to swearing, for in it are many falls' (Ecclesiasticus 23).