Westminster Larger Catechism

Q. 114. What reasons are annexed to the third commandment?

A. The reasons annexed to the third commandment, in these words, The LORD thy God, and, For the LORD will not hold him guiltless that taketh his name in vain, are, because he is the Lord and our God, therefore his name is not to be profaned, or anyway abused by us; especially because he will be so far from acquitting and sparing the transgressors of this commandment, as that he will not suffer them to escape his righteous judgment, albeit many such escape the censures and punishments of men.