Final answer:
Chavez's purpose is to emphasize the dangers of pesticide use and to galvanize support for the UFW's boycott to improve working conditions and promote safer agricultural practices.
Step-by-step explanation:
Cesar Chavez's purpose in the passage from "Lessons of Dr. Martin Luther King, Jr." is to highlight the threat posed by the use of pesticides on crops, specifically table grapes, both to the environment and to human health. He emphasizes the dangers that these pesticides present, not just to farm workers who are exposed directly, but also to consumers who may ingest the residues unknowingly. Chavez uses this argument to raise awareness and galvanize support for the United Farm Workers' boycott against grape growers who refuse to adopt safer practices and recognize the union. By doing so, he is advocating for better working conditions and safer agricultural practices, drawing on the efficacy of consumer boycotts as a means to force change.