RobH_en_tn/psa/062/009.md

men of low standing ... men of high standing are a lie

This refers to men of all levels of wealth and importance. The phrases "are vanity" and "are a lie" have the same meaning. One cannot confidently trust in anyone. Alternate translation: "you cannot place your trust in men, no matter how important they are" (See: rc://en/ta/man/translate/figs-merism and rc://en/ta/man/translate/figs-parallelism)

weighed together, they are lighter than nothing

If you put all of these kinds of men together on a scale, they would have no weight. This means that they have no real value to you.