Calvin takes the Third Commandment and presses it past “don’t swear falsely” into a whole posture of reverence: God’s name must be treated as holy in thought, speech, doctrine, and interpretation, so that we neither trivialize his Word nor slander his works, and especially so that we do not drag his name into careless talk, spiritual theatrics, or manipulative religion (Exodus 20:7). From there he defines an oath as calling God to witness the truth, which makes swearing a kind of worship and explains why perjury is not merely a social sin but a direct profanation of God’s truthfulness (Leviticus 19:12; Joshua 7:19; Isaiah 19:18; Jeremiah 12:16). He then argues that even true oaths can violate the command when they are unnecessary, habitual, or frivolous, and he rejects both the culture of casual swearing and the practice of substituting  ...