Ecclesiastes 4:8
There is one alone, and there is not a second; yea, he hath neither child nor brother: yet is there no end of all his labour; neither is his eye satisfied with riches; neither saith he, For whom do I labour, and bereave my soul of good? This is also vanity, yea, it is a sore travail.
Ecclesiastes was written by Solomon, the son of David and king in Jerusalem, after his unsatisfying experience in wealth and luxury and idolatry when his heart was led away by his many wives. The verse shows the vanity of human life and the utter uselessness of all human pursuits apart from God. It leads to the conclusion that the whole duty of man is to fear God and keep His commandments.