Flaubert knew that rhythm was essential for effective sentences. Good speech writers are also aware of it. A good speech has an almost metrical line, beating out point after point as the speaker builds toward a climax. In the quotation from Lincoln's Second Inaugural Address below, notice how the sentence begins with a series of phrases of approximately equal length. The pauses at the end of each phrase create the rhythm.
With malice toward none; with charity for all; with firmness in the right, as God gives us to see the right, let us strive on the finish the work we are in; to bind up the nation's wounds; to care for him who shall have borne the battle, and for his widow, and his orphan--to do all which may achieve and cherish a just and lasting peace among ourselves, and with all nations.
John F. Kennedy also knew the power of rhythmic sentences. His Inaugural Address begins with a series of phrases. This passage ends with a balanced construction.
Let the word go forth from this time and place, to friend and foe alike, that the torch has been passed to a new generation of Americans, born in this century, tempered by war, disciplined by a hard and bitter peace, proud of our ancient heritage, and unwilling to witness or permit the slow undoing of those human rights to which this nation has always been committed, and to which are are committed today at home and around the world.
Sentences in speech tend to be longer than sentences intended to be printed on a page. The inflections of the speaker's voice can convey feelings and nuances that the printed page cannot. Nevertheless, the writer can learn from the speaker the value of the rhythm and flow of the sentence. William Faulkner was one writer who captured the the flow of the human voice in his writing. This passage from The Sound and the Fury is almost more like poetry than prose.
I could smell the curves of the river beyond the dusk and I saw the last light supine and tranquil upon tideflats likes pieces of broken mirror.
Isak Dinesen was another writer who successfully captured the rhythmic flow of human speech in her writing.
Suddenly, gently, the summits of the hill caught the first sunlight and blushed. Out of Africa