What are rhetorical devices?

What is the purpose of using rhetorical devices?

• I mean it keeps writing interesting but anything else specifically? And what are the purposes of using metonymy and synecdoche? Those are both specific rhetorical devices but that I know the meaning and examples but not sure why we even use them.

• Answer:

  The simplest figure of speech is the SIMILE. A simile emphasizes a similarity of two things by merely saying it: "You are like a dog", or "You are as a dog". The figure rests entirely on one word. A METAPHOR emphasizes a similarity of two things by saying they are the same; "You are a dog". Next comes a big word: HYPOCATASTASIS. This is a Greek word. 'Hypo' means under, as in 'hypodermic', 'cata' means thrown, as in 'catapult', and 'stasis' means standing, as in the sci fi "stasis field" where things are made to stand still. Hypocatastasis is a meaning thrown under, or in plain English, name-calling. Hypocatastasis just calls the fellow "Dog!" See Luke 13:32 "that fox", and Genesis 3:1 "the serpent". A PARABLE is an extended figure of speech; a story based on a simile, metaphor, or hypocatastasis. If the story is possible, it is a MYTH. If the story is impossible, it is a FABLE. A story about talking animals is a fable. If a fable includes an explanation of the meaning, it is an ALLEGORY. Many of Aesop's so-called fables are actually allegories. Don't confuse any of these with LEGEND, which is a supposedly true but unverified historical account (Jonah, for example).