An isocolon is a figure of speech which uses a form of symmetry, creating a pattern in the expression. This is mainly used for rhetorical effect, but has produced a lot of very memorable, grammatically efficient expressions. The pattern also includes some rhythmic elements, because of either consonance or the development of syllable patterns.
Examples of Isocolons:
Vene, vidi, vinci (Julius Caesar) I came, I saw, I conquered|
We will fight them on the beaches, we will fight them in the streets (Winston Churchill)
Ask not what your country can do for you; Ask what you can do for your country. (John F. Kennedy)