In Martin Luther King Jr.'s "I Have a Dream" speech, what is an example of repetition? What is its effect?

There are
many examples of repetition in Martin Luther King Junior's "I Have a Dream" speech.
The repetition serves as emphasis. Since the speech was given orally, the repetition also helps
the audience comprehend his points. It is often more difficult to just hear information than it
is to read or have visual aids, so the repetition helps the audience track with the speech and
King's tenets. In the example below, King repeats the phrase "one hundred years later"
three times. This serves to highlight the fact that it has been a century since Lincoln signed
the Emancipation Proclamation, which freed the slaves, yet black people were still in a type of
bondage. 

But one hundred years
later, the Negro still is not free. One hundred years
later, the life of the Negro is still sadly crippled by the manacles of
segregation and the chains of discrimination. One hundred years
later, the Negro lives on a lonely island of poverty in the midst of a vast ocean
of material prosperity. One hundred years later, the Negro is still
languished in the corners of American society and finds himself an exile in his own land. And so
we've come here today to dramatize a shameful condition.

Perhaps the most famous example of repetition in this speech is the phrase, "I
have a dream." King repeats this phrase as he develops an idea of what his dream entails.
It becomes a type of anthem as he paints a picture of a country in which there is unity and
equality among races. 

I have
a dream that one day even the state of Mississippi, a state sweltering with the
heat of injustice, sweltering with the heat of oppression, will be transformed into an oasis of
freedom and justice.

I have a dream that my four
little children will one day live in a nation where they will not be judged by the color of
their skin but by the content of their character.

I have
a dream today!

Another noteworthy example of repetition in this speech is the repeated phrase
"let freedom ring." This phrase is repeated 10 times and is a rallying cry. He uses it
to proclaim that freedom, as it is expressed in the song "My Country 'Tis of Thee,"
will only be fully realized when there is equality among all races of people. So he repeats the
phrase and calls out many different locations in the country. The locations he mentions span the
whole country and creates a cry for unification.