Final answer:
Jackie Robinson's letter to President Eisenhower warns of the urgency for civil rights reforms and the growing impatience among black Americans, emphasizing the need for government action.
Step-by-step explanation:
The letter from Jackie Robinson to President Dwight D. Eisenhower is significant because it conveys the urgency and impending impatience of black Americans during the Civil Rights era. Robinson's language serves to emphasize how critical it was for the federal government to take action against discrimination and to support civil rights reforms. By describing the determination of black people to achieve equality, Robinson was highlighting the growing discontent among African Americans, thus warning the president that without governmental action, they might resort to more direct forms of protest.