• anaphora: Repetition of the same word or group of words at the beginning of successive clauses, sentences, or lines. (Silva Rhetoricae. rhetoric.byu.edu)

Your first task is to note how King does or does not (1) connect the act of repetition with an expression of power and does or does not (2) connect anaphora with power. [There are of course several kinds of rhetorical repetition, epistrophe is another, and is one that King also uses in these same quoted lines.]

• epistrophe: Ending a series of lines, phrases, clauses, or sentences with the same word or words. (Silva Rhetoricae. rhetoric.byu.edu)

In order to accomplish your task, you must understand what King's message in this quoted passage is. It would seem to be that power is required for social reform and that power is taken to be extremism by those opposing social reform. To make his point, King references some of the most powerful, extremist reformers of all time, beginning with the Prophet Amos and ending with Thomas Jefferson.

[It is interesting that King does not list these extremists in chronological order but rather begins with Jesus, who came after Amos, and ends with Jefferson, who came before Abraham Lincoln; he uses an order of rhetorical importance (which might tie into your topic of power).]

To find your thesis, which no one can find for you, you will have to consider all these details and find what you think the relationship between them is. You might find that you can tie in the epistrophe repetition as well to elaborate upon or to confirm your idea of how anaphora and power relate to each other in this quotation from King's speech.

Anaphora, referencing back to something over and over again, is useful in giving a kind of persuasive rhythm to a speech.  King often uses this technique.  It is like listening to a good Southern preacher.  It rises and falls.  It builds up.  It also adds emphasis.