Albert Barnes Commentary Ecclesiastes 1:3

"What profit hath man of all his labor wherein he laboreth under the sun?" — Ecclesiastes 1:3 (ASV)

What profit ... - The question often repeated is the great practical inquiry of the book; it receives its final answer in (Ecclesiastes 12:13–14). When this question was asked, the Lord had not yet spoken (Matthew 11:28). The word “profit” (or pre-eminence) is opposed to “vanity.”

Hath a man - Rather, has man.