Martin Luther King was a master of oratory. His skill was attributable not just to his speaking skill, but also his ability to use conventional rhetorical devices to great effect.
Early in the speech, King uses the device of repetition (anaphora). He repeats the term “One hundred years later” four times in one section as he describes the condition of the African-American in contemporary society, as in, “But one hundred years later, the Negro still is not free.” This phrase recalls the observation that he had just made regarding the signing of the emancipation proclamation “five-score years earlier.”
Late in the speech, as King is bringing his message to a close, he uses the physical properties of his voice to raise the dramatic effect. Again he uses repetition with the line “Let freedom ring from . . .” and names different American cities. Then, in the speech’s final lines he lifts his voice in climactic crescendo, quoting an old song, “Free at last, free at last, thank God almighty, we are free at last” (epize uxi s).