'Working' in the Bible

Then I saw all the works which my hands had made, and everything I had been working to do; and I saw that all was to no purpose and desire for wind, and there was no profit under the sun.

For what does a person gain from everything that he accomplishes and from his inner life struggles that he undergoes while working on earth?

He has made everything beautiful and appropriate in its time. He has also planted eternity [a sense of divine purpose] in the human heart [a mysterious longing which nothing under the sun can satisfy, except God]—yet man cannot find out (comprehend, grasp) what God has done (His overall plan) from the beginning to the end.

It is one who is by himself, without a second, and without son or brother; but there is no end to all his work, and he has never enough of wealth. For whom, then, am I working and keeping myself from pleasure? This again is to no purpose, and a bitter work.

Sweet is the sleep of a working man, whether he eats a little or a lot, but the excess wealth of the rich will not allow him to rest.

And this again is a great evil, that in all points as he came so will he go; and what profit has he in working for the wind?

Sow your seed in the morning, and don't stop working until evening, since you don't know which of your endeavors will do well, whether this one or that, or even if both will do equally well.