Shorter Catechism Q. 55. What is forbidden in the third commandment? A. The third commandment forbiddeth all profaning or abusing of anything whereby God maketh himself known.
Commentary: How might we profane or abuse God’s name or “anything whereby God maketh himself known”? One way is to invoke God’s name to confirm a lie (e.g., we lie and then say, “I am telling the truth, so help me God”), because then we are making God a party to our lie and using him for our evil purposes.
Another way to misuse God’s name is to speak in his name falsely. If we want to push our own agenda on people who love God or to get them to agree with us, then there is no better way to do it then to say something like this: “God is for this” or “God is on the side of” or “God told me to do this” or “This is a God thing” or “The Holy Spirit is leading me to do this.” We, however, mustn’t use God’s name to get what we want or to justify our actions, unless we can demonstrate that God has spoken on the matter from Scripture.
A third way to misuse God’s name is to embrace an ungodly lifestyle. We profane the name of the Lord when we claim to be a Christian but act like a pagan (Lev. 18:21; Prov. 30:8-9; Amos 2:7). Moreover, we will cause others to revile God as well (Rom. 2:24). For other ways we can misuse God’s name see Westminster Larger Catechism 113.