"Five score years ago, a great American, in whose symbolic shadow we stand today, signed the Emancipation Proclamation."
“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 the content of their character.”
"But one hundred years later, the Negro is still 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."
King alludes to the Emancipation Proclamation which in turn alludes to Abraham Lincoln who was the first person to try and give some basic rights to black people in the United States. This establishes huge credibility with the audience as they all know, support, and admire Lincoln and his great contributions to the only rights and freedoms they possess now.
To appeal to the audience's emotions, King talks about his personal life and his own little children. He wants the audience to be able to understand how important and serious this issue is for his young kid's futures and theirs. Everyone in the audience with children of their own felt something when he said this.
At this point, King pulls out the undeniable facts that even after the Emancipation Proclamation was signed, one hundred years later, they still do not have the basic rights and freedoms granted to all Americans. King emphasizes one hundred years to show just how long they have been denied their rights as "citizens" of the United States.