To pronounce God's name without a good reason for doing so is to take it in vain.
"Secret Societies" by David MacDill, Jonathan Blanchard, and Edward Beecher
One day, in the open street, a knight began to swear and take God's name in vain.
"The Life of Joan of Arc, Vol. 1 and 2 (of 2)" by Anatole France
He, his grandfather's grandson, was going to thrash a foolish boy for taking his grandfather's name in vain!
"An Australian Lassie" by Lilian Turner