Answer:
That they are friends and not enemies. And they must not be enemies
Explanation:
Following the victory of Abraham Lincoln as the President of the United States in 1860. There were widespread worries, most especially among the Southern states.
The worry was based on the fact that Abraham Lincoln was a Republican and he could threaten their hold on slavery use. Starting with South Carolina the first state to declare itself out of the union. South Carolina's actions were followed by another Six States.
This forced Abraham Lincoln to deal with the issue in his first inaugural address. He listed various reasons for the states not to secede.
However, Lincoln’s strongest argument as to why the South should not "that they are friends and not enemies. And they must not be enemies."
This was evident in the last paragraph of the address, where it was stated that "We are not enemies, but friends. We must not be enemies. Though passion may have strained it must not break our bonds of affection..."