Final answer:
The first inaugural address by Lincoln focused on saving the Union and preventing the Civil War, offering both a warning and a plea for unity. In contrast, the second inaugural was delivered during the Civil War and reflected upon the war's significance and the need for healing after the conflict.
Step-by-step explanation:
The difference between Lincoln's first and second inaugural addresses stems from the evolving context of the nation. In his first inaugural address, Lincoln sought to calm fears in the South about his stance on slavery and secession, making a strong case for the permanent nature of the Union and appealing for national unity. His words were aimed at saving the Union and averting civil war.
However, by the time of the second inaugural, the Civil War had been raging for four years, and Lincoln's approach was different; he pondered the war's causes and meanings and presented a more somber and reflective narrative that looked toward healing and reconciliation in the post-war period.