To take up God’s name in vain means any frivolous, or insincere, or thoughtless, or unsubstantial use of His name. It might mean irreverent humor which mocks God in speech, or mocks others with His name. It might be blasphemy or cursing or a broken oath, but it means more than that. It could mean professing faith in Christ, and claiming to be a Christian, and receiving baptism, and yet walking in worldliness.