The Third Commandment

Q99. What is required in the third commandment?
A. We are not to blaspheme or to abuse the Name of God by cursing, perjury, or unnecessary oaths, nor to share in such horrible sins by being silent bystanders. In short, we must use the holy Name of God only with fear and reverence, so that we may rightly confess Him, call upon Him, and praise Him in all our words and works.

Q100. Is the blaspheming of God's Name by swearing and cursing such a grievous sin that God is angry also with those who do not prevent and forbid it as much as they can?
A. Certainly, for no sin is greater or provokes God's wrath more than the blaspheming of His Name. That is why He commanded it to be punished with death.

Q101. But may we swear an oath by the Name of God in a godly manner?
A. Yes, when the government demands it of its subjects, or when necessity requires it, in order to maintain and promote fidelity and truth, to God's glory and for our neighbour's good. Such oath-taking is based on God's Word and was therefore rightly used by saints in the Old and the New Testament.

Q102. May we also swear by saints or other creatures?
A. No. A lawful oath is a calling upon God, who alone knows the heart, to bear witness to the truth, and to punish me if I swear falsely. No creature is worthy of such honour.