Thou shalt not take the name of the Lord thy God in vain; for the Lord will not hold him guiltless that taketh his name in vain.
Taking in vain, as being to profane and blaspheme. By “taking the name of God in vain” is properly signified to turn truth into evil, that is, to believe that it is truth, and nevertheless to live in evil; and it also denotes to turn good into falsity, that is, to live holily, and yet not to believe. Both are profanation for believing is of the understanding, and living is of the will.
We should not also profane or blaspheme things which are of the Word, or of the doctrine of faith, thus which are holy, and not hold them in derision, or debased them to unclean earthly things, and thus defiled them.
The word guiltless means no forgiveness unless one repents both in his understanding and of his will.
When one mention a name it represent the whole quality of that person, thus with The Lord it represents all that is holy, the things of love, mercy compassion, truth, order and many other qualities of The Lord.
Profanity is characterized by irreverence or contempt for God or sacred principles or things; or being irreligious.