Prose is use of language in a higher plane than the language used in conversation or writing of educated common people. Higher plane does not mean high sounding or archaic words.
The best known description of ‘good English’ is “proper words at proper places”. No two words mean exactly the same. A word gets meaning only from its context. Without the context word is meaningless. Language is a convention of using each word only in its context. Mingling words of older classical days with ultra modern vocabulary is futile unless it is used for a specific effect. Using substitutes to suit rhyme or for variety is not appreciated.
Also read: Subjugation of Executive
Here are a few examples of widely appreciated prose.
“Men fear death as children fear to go in darkness.”
“Revenge is a kind of wild justice.”
“I have no belief in belief.”
My teacher spoke for an hour on each of these sentences.
Also read: “Copying – Corruption”