In the Atlanta speech, Washington repeatedly uses his, “Cast Down a Bucket” analogy. What is the message behind this?

From what I remember, "Cast Down a Bucket" had to do with Washington's plea that white southerners and African Americans needed to work together. It was a plea based on history and nostalgia, and it came at a time when massive immigration was taking place. At this time, blacks were passed over in favor of white immigrants workers.