10 You applaud what is now said, but when you have amended, you will applaud in a greater degree not only us, but also yourselves; and you will hear with more pleasure what is spoken; and you will call upon God with a pure conscience, who is so sparing of you, O man! That He says, “Neither shall you swear by your head.” But thou so despisest Him as to swear even by His glory. “But what shall I do,” says one, “with those who impose necessity on me?” What kind of necessity can there be, O man?
Let all men understand that you will choose to suffer anything rather than transgress the law of God; and they will abstain from compelling you. For as a proof that it is not an oath which renders a man worthy of credit, but the testimony of his life, the uprightness of his conversation, and his good reputation, many have often split their throats with swearing, and yet have been able to convince no one; whereas others by a mere expression of assent, have been esteemed more deserving of belief than they who swore never so much.
Knowing, therefore, all these things, and placing before our eyes the punishment that is in store for those who swear, as well as for those who swear falsely, let us abstain from this evil custom, that advancing from hence to the correction of what remains, we may enjoy the blessedness of the life to come, which God grant that we may all be found worthy to obtain, by the grace and love toward man of our Lord Jesus Christ, through Whom and with Whom to the Father with the Holy Ghost be glory, and power, and honour, now and ever, and world without end. Amen.
Source: Homilies on the Statues (New Advent)