From a post on GOD’s Children Group on Facebook (posted June 10, 2017):

But even though a person sins a hundred times and still lives a long time, I know that those who fear God will be better off. Ecclesiastes 8:12
So I recommend having fun, because there is nothing better for people in this world than to eat, drink, and enjoy life. That way they will experience some happiness along with all the hard work God gives them under the sun.
Ecclesiastes 8:15
​It is hard work to live and work the works of the FATHER. John 9:4, 16:33
But with that work, done from a genuine heart, comes joy and unspeakable blessings. 
In essence, fun comes from living out your purpose on earth (doing GOD’s work.)
Couldn’t have said it better myself. 😉