"You shall not misuse the name of the Lord your God, for the Lord will not hold anyone blameless who misuses his name." (NIV)
Like Rami, I have childhood memories associated with the text. In my case, most adults assumed the commandment prohibited cursing ("cussing," as we might say in the South)that used the term "God." Some of the more strict among us argued the prohibition extended to such expressions as "gosh dang it," "golly," or just about any expression of anger, amazement or ill will that began with the letters "g" and "o."
Amazing, isn't it? Even as a child I thought it unlikely God had slipped such a trivial matter into something so important as the Ten Commandments.
What does it mean to "take the name of the Lord your God in vain," as the KJV puts it? My personal paraphrase of the phrase is: "You shall not tie God's name to ungodly things." To put it another way, do not claim God endorses that which is evil. The prohibition is coupled with a warning: God will not hold you blameless, let you off the hook, etc. if you do so.
Observing the commandment is difficult. To do so requires that we nurture both our knowledge of the living God (whatever the limits of such knowledge may be) and our openness to his presence. Such knowledge and relationship engenders "holy caution," that is a growing awareness of how seldom we dare say, "Thus says the Lord."
Yet by its very existence, the commandment acknowledges we will face times when we must speak. The moment we do so, the commandment shifts from the private to the public sphere. In the American south, the story of many white preachers and their support first of slavery and then of segregation provides the prime cautionary tale. Similiary, the story of black and (a few) white preachers who challenged the system and offered an alternative vision of equality serves as a hope-filled contrast.
Much more needs to be said about possible applications of the commandment in private life, but that's for another posting.