Ecclesiastes 3

Solomon asked -

"What profit hath he that worketh in that wherein he laboureth?" (Old Testament | Ecclesiastes 3:9)

In my opinion, the tone in Ecclesiates seems to be a little bit pessimistic and he ponders the things of this world using the words "under the sun". But even then Solomon answers -

"I have seen the travail, which God hath given to the sons of men to be exercised in it.
11 He hath made every thing beautiful in his time: also he hath set the world in their heart, so that no man can find out the work that God maketh from the beginning to the end.
12 I know that there is no good in them, but for a man to rejoice, and to do good in his life.
13 And also that every man should eat and drink, and enjoy the good of all his labour..." (Old Testament | Ecclesiastes 3:10 - 13)

And then of labour the good that comes from labor, Solomon states -

"...it is the gift of God." (Old Testament | Ecclesiastes 3:13)

Work and the satisfaction we receive from it tends to bring man joy and satisfaction -

"Behold that which I have seen: it is good and comely for one to eat and to drink, and to enjoy the good of all his labour that he taketh under the sun all the days of his life, which God giveth him: for it is his portion.
19 Every man also to whom God hath given riches and wealth, and hath given him power to eat thereof, and to take his portion, and to rejoice in his labour; this is the gift of God." (Old Testament | Ecclesiastes 5:18 - 19)