Pay close attention to the references and metaphors he employs. His use of language is incredibly rich, no term or phrase is included accidentally!
1963, the speech is delivered on the steps of the Lincoln Memorial in Washington, DC. This is important! Abraham Lincoln, the 16th President of the United States, signed the Emancipation Proclamation in 1863 which officially made the practice of slavery illegal in the country. The first few lines of the speech, 'five score years ago' reference the first few lines of the Gettysberg Address (1863), the most famous speech given by Lincoln (score=multiple of 5). Consider the location and historical moment of the speech.
“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.”
Why does he use the term poverty on one hand, and material prosperity on the other? Why does he specify material prosperity?
The metaphor of debt---
“In a sense we've come to our nation's capital to cash a check. When the architects of our republic wrote the magnificent words of the Constitution and the Declaration of Independence, they were signing a promissory note to which every American was to fall heir. This note was a promise that all men, yes, black men as well as white men, would be guaranteed the "unalienable Rights" of "Life, Liberty and the pursuit of Happiness." It is obvious today that America has defaulted on this promissory note, insofar as her citizens of color are concerned. Instead of honoring this sacred obligation, America has given the Negro people a bad check, a check which has come back marked "insufficient funds."
But we refuse to believe that the bank of justice is bankrupt. We refuse to believe that there are...