"If someone now asks, “How do you understand the Second Commandment?” or “What is meant by taking God’s name in vain, or misusing God’s name?” answer briefly in this way: “It means misusing God’s name when we call upon the Lord God—no matter how—in order to deceive or do wrong of any kind.” Therefore, this commandment makes this point: God’s name must not be appealed to falsely, or taken upon the lips, while the heart knows well enough—or should know—that the truth of the matter is different. This is what happens with people who take oaths in court, where one side lies against the other. For God’s name cannot be misused worse than for the support of falsehood and deceit. Let this remain the exact German and simplest meaning of this commandment."
Want the Large Catechism for yourself? Call Concordia Publishing House at 1-800-325-3040. I recommend you get the newer version item #223116. It has helpful study questions at the end of each section.
Quote from "Concordia : The Lutheran Confessions" 2005 (Edited by Paul Timothy McCain) (364). St. Louis, MO: Concordia Publishing House.