How is repetition structure or parallel structure used to describe syntax?

Question

How is repetition structure or parallel structure used to describe syntax?

Answer 1

Parallel structure is a kind of syntax or sentence structure.  Parallel structure is noted by the same formation of sentences (or syntax).  Thus, syntax is used to describe/form parallel structure

The most famous example of parallel structure is "Ask not what your counry can do for you but what you can do for your country."