Learn English – the word to describe a single object to represent the many

Allegory

1. a poem, play, picture, etc, in which the apparent meaning of the characters and events is used to symbolize a deeper moral or spiritual meaning 2. the technique or genre that this represents 3. use of such symbolism to illustrate truth or a moral 4. anything used as a symbol or emblem

The literary device is known as a 'Symbolism in literature' or a variant.

The symbolist movement in literature / by Arthur ... . Symons, Arthur, 1865-1945 states:

Symbolism in literature really is: a form of expression, at the best but approximate, essen- tially but arbitrary, until it has obtained the force of a convention, for an unseen reality ap- prehended by the consciousness. It is some- times permitted to us to hope that our conven- Rtion is indeed the reflection rather than merely the sign of that unseen reality.

Stream of consciousness is, I think, what you are referring to.

• Stream of consciousness is a narrative mode, or device, that seeks "to depict the multitudinous thoughts and feelings which pass through the mind. Another term for it is 'interior monologue'."

(Wikipedia)