Q. 99. What is required of the third commandment?
That we, not only by cursing or perjury, but also by rash swearing, must not profane or abuse the name of God; nor by silence or connivance be partakers of these horrible sins in others; and, briefly, that we use the holy name of God no otherwise than with fear and reverence; so that He may be rightly confessed and worshipped by us, and be glorified in all our words and works.
 Leviticus 24:11 and 19:12; Matthew 5:37; Leviticus 5:4;  Isaiah 45:23–24;  Matthew 10:32;  1 Timothy 2:8;  1 Corinthians 3:16–17.
Q. 100. Is then the profaning of God’s name, by swearing and cursing, so heinous a sin, that His wrath is kindled against those who do not endeavour, as much as in them lies, to prevent and forbid such cursing and swearing?
It undoubtedly is, for there is no sin greater or more provoking to God, than the profaning of His name; and therefore He has commanded this sin to be punished with death.
 Leviticus 5:1;  Leviticus 24:15.
The Third Commandment is: “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” (Ex 20:7). What does it mean to take the name of God in vain? It means using the names, titles or attributes of God in such a way as to empty it of meaning. When do we use the name of God in our daily life? We use it legitimately in vows and oaths. A vow is a promissory oath. Now, when we take an oath, what we are in effect doing is to call upon God not only to be our witness to what we say, but to chastise or punish us if we should break our word. This being the case, a person who tells a lie under oath (i.e., perjures) is taking the name of God in vain in a very heinous way, for he would in essence be using God’s holy name to bolster his lie and therefore showing contempt to God. And contemptuously challenging Him to defend the honour of His name.
Another way which the world uses the name of God in vain is to curse and swear in His name. There is of course legitimate swearing, which is the same as vows and oath, but there is also abusive swearing. Abusive swearing or cursing always involves the vain use of the name of God because it calls upon God to curse or punish some one as if God is obliged to do as commanded. But the worst form of using the name of God in vain must be to use the name of God as a swear-word or even an interjection. Those who do so would often claim that they mean no offence, or that they say their interjection or swear-word without thinking. But this does not in anyway diminish the severity of their offence against God, for it would indeed be emptying the name of God of its meaning.
Are Christians guilty of breaking the Third Commandment too? Certainly, and four of the most common ways are: (1) Failing to speak up or, worst, feeling no offence when someone we know uses the name of God or the name of Christ as a swear-word. (2) Using the name of God flippantly in exclamations, such as: “My God!” or “My Goodness!” (3) Using the name of God as punctuation in prayer; example: “Lord God, help me, Lord; Lord God, I am in distress, Lord, I know you can help, Lord God, for, Lord God, you can do all things, Lord.” (4) Singing the name of God without reverence or understanding.
Heidelberg Catechism >