2 Let us not then be desponding; nor let us despair of a change for the better; but let us hope that speedily there will be a calm; and, in short, casting the issue of all the tumults which beset us upon God, let us again handle the customary points; and again bring forward our usual topic of instruction. For I am desirous to discourse to you further concerning the same subject, to the end that we may radically extirpate from your souls the wicked practice of oaths.
Wherefore it is necessary for me again to have recourse to the same entreaty that I made before. For lately I besought you, that each one taking the head of John, just cut off, and the warm blood yet dripping from it, you would thus go home, and think that you saw it before your eyes, while it emitted a voice, and said, “Abhor my murderer, the oath!” What a rebuke did not effect, this an oath effected; what a tyrant's wrath was insufficient for, this the necessity of keeping an oath brought about!
And when the tyrant was publicly rebuked in the hearing of all, he bore the censure nobly; but when he had thrown himself into the fatal necessity caused by oaths, then he cut off that blessed head. This same thing, therefore, I entreat; and cease not entreating, that wherever we go, we go bearing this head; and that we show it to all, crying aloud, as it does, and denouncing oaths. For although we were never so listless and remiss, yet beholding the eyes of that head fearfully glaring upon us, and threatening us if we swear, we should be more powerfully kept in check by this terror, than by any curb; and be easily able to restrain and avert the tongue from its inclination toward oaths.
Source: Homilies on the Statues (New Advent)