This book is a real eye-opener. Studies of Southern generals in the Civil War generally fall under the spell of the Cult of Robert E. Lee. Alexander makes the case that Jackson was a true military revolutionary who grasped better than anyone else in the Rebel command the modern circumstances of war and how the tactics and methods of the time were hopelessly obsolete. Lee is depicted as a capable, and well-meaning, but outdated commander.
Jackson understood that the rifle had changed everything. Offense had ceded the advantage to defense. Jackson knew that massed ranks could not be withstand concentrated rifle and cannon fire. Jackson therefore repeatedly insisted that the Confederates, who were outgunned and had a weaker industrial infrastructure, should place their army in a strategic position where the Union had to attack them (such as between DC and Philadelphia). Then, on ground of their choosing, the Rebels would destroy the attacking Union armies and then counterattack. Repeatedly, Lee declined this advice, instead choosing to attack the Union wherever they happened to be.
As someone who feels that the nation benefited by the South's defeat, I'm glad Lee never listened to Jackson, otherwise the outcome of the war might have differed.