Which literary element does an author use to provide a deeper meaning to a story?

There are a variety of literary devices.

Each have to be applied correctly to achieve it's intended effect. One literary element which can be used by an author to provide deeper meaning to a story is Symbolism.

When an emblem is used to signify ideas and qualities, by giving them symbolic meanings that are different from their literal sense this is known as Symbolism.  Generally, it is an object representing another, to give an entirely different meaning that is much deeper and more significant.

For example:

Used in sentences they come out like this:

Cheers!

a conclusion based on evidence is an example of a. inference