The commandment which some people mistakenly quote as "using the Lord's name in vain," does not mean using his name in an oath or even a swear word (though that would be unseemly for a Christian, or anyone for that matter). This commandment was not intended (by context and historical use) to be limited to a single category of offense. It seems to be intentionally broad in character. The Old Testament consistently speaks of the importance of God's "name". God equates his "name" with his person and character.
What the commandment means, "Taking His name in vain" is this:
When you call yourself a "Christian" then you are taking the name of the Lord, (Christ). This is akin to a woman "Taking" the last name of her husband when they marry.
When you "Take the Lord's name" by calling yourself a Christian, then you should do your best to follow his teachings and precepts in your daily life and be as Christ-like as you can by remembering what it was that He taught us about Loving one another, helping the poor and downtrodden, feeding the hungry, clothing those who have no clothes, being truthful, caring for the sick, being good and kind, etc.
When you don't do these things but rather lie, cheat, steal, act selfishly, deliberately hurt others, bear false witness against others, etc. and still call yourself a Christian then you have "Taken the Lord's name in vain."