How does Kennedy gain authority by quoting Abraham Lincoln at the end of "Among Free Men"?

Quoting Abraham Lincoln links Kennedy’s message to a leader who is widely admired and respected. This borrowed credibility strengthens Kennedy’s authority by suggesting that his ideas belong to a tradition of American leadership. The quote is not mainly about Lincoln’s speaking ability or a direct comparison with the Civil War; its main effect is to associate Kennedy’s ideas with someone many Americans consider great.

AI-written and checked against the verified answer.