Answer:
The central idea of Lincoln's speech was to show the American public that the nation must stay united and tell Southerners that secession was illegal. Lincoln says, "Plainly the central idea of secession is the essence of anarchy." Through this statement, he demonstrates that the Southern states' attempt to separate from the Union is a breach of law and order. He also argues that the US Constitution is permanent and cannot be dissolved. There are no terms in the Constitution that allow the dissolution of its government:
Perpetuity is implied, if not expressed, in the fundamental law of all national governments. It is safe to assert that no government proper ever had a provision in its organic law for its own termination.
Lincoln also reassures Southerners that his Republican administration would not interfere in matters related to slavery and its laws:
I have no purpose, directly or indirectly, to interfere with the institution of slavery in the States where it exists. I believe I have no lawful right to do so, and I have no inclination to do so.
He tries to calm the anxious Southerners by telling them that he is committed to upholding their states' rights:
. . . the property, peace, and security of no section are to be in any wise endangered by the now incoming Administration. I add, too, that all the protection which, consistently with the Constitution and the laws, can be given will be cheerfully given to all the States when lawfully demanded, for whatever cause—as cheerfully to one section as to another.
