"You shall not take the name of the LORD your God in vain,
for the LORD will not hold him guiltless who takes his name in vain."
(Exodus 20:7)
After His existence as the only true God, God moves onto His name. We should not take the Lord's name in vain. What does the phrase "in vain" mean? Primarily, it means using His name uselessly or carelessly. Like many of us, God doesn't want His name to be used in such a way that it shows that we don't care or need Him.
He also tells us through this commandment how we should treat His name. He commands us to call upon His name in every trouble, pray, praise, and give thanks. God gives us His name so that we can use it properly. We do that when we pray to Him for guidance in our lives in good times and bad.
Using God's name uselessly, He will not hold you guiltless. Guiltlessness only comes through repentance. Repentance starts as we pray "Hallowed by Thy name". Amen.