Why did Dr. king have a forum for giving his speech?

First of all, Dr. Marin Luther King, Jr. gave a remarkable speech on August 28, 1963 called "I have a dream".  His goal was end racism in America, and fight for civic right.  This speech is about 17 mins long located at Lincoln Memorial Washington DC to over hundreds of thousands audience.  This is a very famous speech Dr. King begun his speech by telling how black people were treated unfairly and how did America had treat her people badly.
Martin Luther King, Jr. gave "I have a dream" speech in front of Lincoln Memorial, President of The United State, Abraham Lincoln a man who supports civic right abandon slavery.  Dr. King was giving a speech which shared the same idea with President Lincoln, therefore Dr. King chose a idea place and given a great speech that remind all the people in the America that black people shall no longer suffer from discrimination.