William S. Plumer, The Ten Commandments.
Anything relating to the true God – His being, His nature, His will, His works, His worship, His service, or His doctrine – pertains to God's name. This commandment extends to the state of men's thoughts and hearts – as well as to their speech. To take God's name in vain, is to use it in any frivolous, false, inconsiderate, irreverent, or otherwise wicked manner. The scope of this commandment is to secure the holy and reverent use of all that by which God makes Himself known to His people; and so to guard His sacred name against all that is calculated to make it contemptible. The manner of taking His name is to be grave, solemn, intelligent, thoughtful, sincere, and with godly fear.
William S. Plumer, The Ten Commandments.