Short Answer 
Allusion is a figure of speech that connects familiar concepts to new ideas, enriching the text and enhancing reader understanding. It serves to engage the audience by linking current arguments to historical precedents, as demonstrated by King, who uses allusion to underscore the significance of social change efforts.
Step 1: Understand the Concept of Allusion
Allusion is a figure of speech that allows writers to reference things, people, and places without explicitly stating them. This technique enriches the text by making connections between familiar concepts and new ideas. It helps the reader make associations and deepens their understanding of the content.
Step 2: Recognize the Purpose of Allusion in Communication
An allusion serves as a tool to extend the reader’s attention and understanding by associating one concept with another. By referencing historical events or figures, a writer can illustrate a parallel or contrast with their current argument or action. This enhances the overall message of the piece and engages the audience more effectively.
Step 3: Analyze King’s Use of Allusion for Historical Precedence
In the context of his actions, King employs allusion to demonstrate that there have been historical events similar to his efforts aimed at generating significant social change. By drawing these parallels, he establishes a precedent that reinforces the legitimacy and necessity of his cause, thereby urging the audience to reflect on the importance of these historical contexts.