Alexander Stephens is, all things considered, a minor figure in American history. He was not the first or most significant secessionist nor did he distinguish himself in the Confederate government. What he was, however, was one of the most forthright and lucid defenders of secession, and it's for this reason that his "Cornerstone Speech" remains an important document for grasping the nature of the Confederacy and Confederate ideology.
In particular, you can think of Confederate constitutional thinking as a road not taken in American political development, an attempt to “re-found” the United States on antifederalist principles, with an explicit commitment to white supremacy. If the politics and political theory of the Confederacy are worth studying—and I believe they are—it is because they embody a reactionary tendency in American political history that still weighs on our society.