From the Heidelberg Catechism for the Lord’s Day, September 15

Third Commandment

“You shall not take the name of the LORD your God in vain, for the LORD will not hold him guiltless who takes His name in vain.

99. What is required in the third Commandment?

That we must not by cursing, or by false swearing, nor yet by unnecessary oaths, profane or abuse the name of God; nor even by our silence and connivance be partakers of these horrible sins in others; and in summary, that we use the holy name of God in no other way than with fear and reverence, so that He may be rightly confessed and worshiped by us, and be glorified in all our words and works.

100. Is the profaning of God’s name, by swearing and cursing, so grievous a sin that His wrath is kindled against those also who do not help as much as they can to hinder and forbid it?

Yes, truly,for no sin is greater and more provoking to God than the profaning of His name; wherefore He even commanded it to be punished with death.