The phrase "vain things" refers to anything that is pointless, useless, or without purpose.
Sentences with «vain things»
No shaking from anxiety and thinking of vain things inside the head, but rather relaxed & in the moment — which is a recipe for success in any date or relationship. (supernutritionlife.com)
«Act 4:25 - 26 Who by the mouth of thy servant David hast said, Why did the heathen rage, and the people imagine vain things? (religion.blogs.cnn.com)