(1.) To utter the name of God unnecessarily in our common conversation.
(2.) To read the Bible carelessly, or to pray without attention and
devotion.
(3.) To swear otherwise than when required by the law to do so, as,
e.g., in courts of law.
(4.) To swear when we are not fully convinced of the truth of our
declaration.
The additional sentence, “for he will not hold him guiltless who taketh
his name in vain,” is to remind us that it is against God the
Omniscient that we sin in breaking this commandment. God knows our
innermost thoughts, whether we think of what we utter or not; whether
we are convinced of what we declare on oath or not. He will punish us
if we break His commandments, although we may be able to conceal our
sins from men and escape condemnation by a human tribunal.