Heidelberg Catechism - Lord's Day 36

99. Q . What is the aim of the third commandment?
       A. That we neither blaspheme nor misuse the name of God by cursing, perjury, or unnecessary oaths, nor share in such horrible sins by being silent bystanders.
In summary, we should use the holy name of God only with reverence and awe, so that we may properly confess God, pray to God, and glorify God in all our words and works.

100. Q . Is blasphemy of God’s name by swearing and cursing really such serious sin that God is angry also with those who do not do all they can to help prevent and forbid it?
       A. Yes, indeed. No sin is greater or provokes God’s wrath more than blaspheming his name. That is why God commanded it to be punished with death.