What did Martin Luther King, Jr mean when he used banking metaphors in his speech at the March on Washington?

In his speech at the March on Washington, best known for his "dream," King described the United States as having "defaulted" on a "promissory note insofar as her citizens of color are concerned." By this King meant that the United States was founded on the promise that all men were created equal, and that everyone in the nation, including African-Americans, was entitled to equality under the law and equality of opportunity. This "promissory note" was...

In his speech at the March on Washington, best known for his "dream," King described the United States as having "defaulted" on a "promissory note insofar as her citizens of color are concerned." By this King meant that the United States was founded on the promise that all men were created equal, and that everyone in the nation, including African-Americans, was entitled to equality under the law and equality of opportunity. This "promissory note" was first issued in the Declaration of Independence and reiterated in the Thirteenth, Fourteenth, and Fifteenth Amendments. But it was one that was clearly not being honored, as Jim Crow laws, discrimination in voting, and de facto segregation in American cities effectively made African-Americans second-class citizens. So when King said at the March that "we have come to...cash a check" he meant that the purpose of the Civil Rights Movement was to force the federal government, and American society as a whole, to live up to its promise of equality for all Americans. It was a powerful rhetorical turn, because it emphasized that for King, the Civil Rights Movement was not about asking for charity. It was about claiming things that all Americans were entitled to, or forcing (not requesting) the United States to honor its obligations. In the context of the march, this meant passing federal civil rights legislation.