This guy knew how to write a speech.

Dr. King often used repetition and parallel construction to great emotional effect when he spoke. There isn't quite as much of that in "Letter From Birmingham Jail," but it still pops up a couple of times. Most notably in paragraph 12, where he repeatedly begins phrases with the word "when":

Perhaps it is easy for those who have never felt the stinging darts of segregation to say, "Wait." But when you have seen vicious mobs lynch your mothers and fathers at will and drown your sisters and brothers at whim; when you have seen hate filled policemen curse, kick and even kill your black brothers and sisters; when you see the vast majority of your twenty million Negro brothers smothering in an airtight cage of poverty in the midst of an affluent society; when you suddenly find your tongue twisted and your speech stammering as you seek to explain to your six year old daughter why she can't go to the public amusement park that has just been advertised on television, and see tears welling up in her eyes when she is told that Funtown is closed to colored children, and see ominous clouds of inferiority beginning to form in her little mental sky, and see her beginning to distort her personality by developing an unconscious bitterness toward white people; when you have to concoct an answer for a five year old son who is asking: "Daddy, why do white people treat colored people so mean?"; when you take a cross county drive and find it necessary to sleep night after night in the uncomfortable corners of your automobile because no motel will accept you; when you are humiliated day in and day out by nagging signs reading "white" and "colored"; when your first name becomes "n*****," your middle name becomes "boy" (however old you are) and your last name becomes "John," and your wife and mother are never given the respected title "Mrs."; when you are harried by day and haunted by night by the fact that you are a Negro, living constantly at tiptoe stance, never quite knowing what to expect next, and are plagued with inner fears and outer resentments; when you are forever fighting a degenerating sense of "nobodiness"—then you will understand why we find it difficult to wait. (12)

Whew.

We included this long passage to show how this repetition builds and builds (and builds) the emotional case he's making about how the Black community can't possibly wait any longer for justice. This cascade of examples makes the idea of waiting absurd, and by the time the sentence finally ends with "then you will understand…" there's a very well established understanding.

We get it, Dr. King.

(Probably because of the repetition.)