'Undertakes' in the Bible

What does a man gain from all of the work that he undertakes on earth?

What benefit does the worker gain from what he undertakes?

moreover, every person should eat, drink, and enjoy the benefits of everything that he undertakes, since it is a gift from God.

I have concluded that everything that God undertakes will last for eternity nothing can be added to it nor taken away from it and that God acts this way so that people will fear him.