What is a "parallel antithesis" sentence?
"It was the best of times, it was the worst of times..." -Charles Dickens
Antithesis literally means the opposite. So, a sentence with antithesis merely puts two opposite ideas together in a sentence to achieve a contrasting effect.
Antithesis emphasizes the contrast through the use parallel structures in the contrasted phrases. The phrases are similar to draw the attention of the reader.
In the above example, the antithesis is it simultaneously being the "best" and "worst" of times. The parallel structure merely draws emphasis to both.