Behold, all ye yourselves have seen it; why then are ye thus altogether vain? Ye yourselves have seen it - Your own experience and observation have shown you that the righteous are frequently in affliction, and the wicked in affluence.
Why then are ye thus altogether vain? - The original is very emphatical: הבל תהבלו hebel tehbalu, and well expressed by Mr. Good: "Why then should ye thus babble babblings!" It our language would allow it, we might say vanitize vanity.