CoP 3 research Story through Sound?

I decided to look into storytelling through sound because sound is an important part of film.

There are three parts to sound in film.
- The human voice
- Sound effects.
- Background music.

The Human Voice.
One of the most important, as this is the way the character/actor tells the story and expresses feelings and motivations.  Often with film the audience perceives little to no difference between character and actor due to the characterisation.

Sound Effects.
These can be used to add mood or atmosphere to the scene of the film, an example would be explosions noises when a bomb goes off to add more emphasis.

Background Music.
In film this is used to describe what the mood of the scene is, e.g. A kissing scene, would have a sweet romantic song playing.

Why do we have sound in film,  In reality there is no background music depicting our actions or moods therefore why is it a key part of storytelling in films?
It's stated here in different blogposts that sound is there to help guide how the audience should feel, referencing back to neuroscience and how the brain becomes involved with the film, this is possibly doing the same thing but enhancing this effect more and making the audience enjoy the film more, and the storytelling.
Clearly this will need to be added to my dissertation as a part of storytelling!