The correct difference between the two passages is:
King believes some tension is necessary, while Lincoln calls for unity.
In "The Gettysburg Address," Lincoln emphasizes the importance of national unity and healing after the Civil War, calling for a "new birth of freedom." In contrast, in "Letter from a Birmingham Jail," King argues that tension and peaceful protest are necessary to bring about social change and justice, as he believes that nonviolent conflict is essential in the struggle against injustice.