Here is a tale from a video game. Sheogorath is a god, a so-called Daedric Prince, whose sphere is Madness, and whose motives are unknowable.
In the earliest of days, in a time when the world was still raw, Sheogorath decided to walk amongst the mortals. He donned his guise of Gentleman With a Cane, and moved from place to place without being recognized. After eleven days and eleven nights, Sheogorath decided that life among mortals was even more boring than his otherworldly existence.
"What can I do to make their lives more interesting?" he said to himself. At that same moment, a young woman nearby commented wistfully to herself, "The sounds of the birds are so beautiful."
Sheogorath silently agreed with her. Mortals could not make the beautiful and inspired calls of birds. Their voices were wretched and mundane. He could not change the nature of mortals, for that was the purview of other Daedric Princes. However, he could give them tools to make beautiful sounds.
Sheogorath took hold of the petulant woman and ripped her asunder. From her tendons he made lutes. From her skull and arm bones he made a drum. From her bones he made flutes. He presented these gifts to the mortals, and thus Music was born.
I don't see why the is being used in those two sentences. The definite article doesn't seem to be describing any specific mortals.
There was an answer about half a month ago:
I was in the N.Y. Library. I was reading the books there, and one book interested me.
This sentence treats "the books" as a single fixture in the New York Library. That doesn't make sense if you're reading them; it makes sense in a context like this:
The yearly cost to insure the books in the New York Library is over a million dollars.
As in the above example, is the article in my text referring to all mortals as a single entity (i.e. not individually)?