I tend to be an "actions speak louder than works" kind of person. I think that, had the outcome of the war been different, maybe this speech would have meant nothing. I am not wholly convinced by his thesis that this one, very short speech totally changed most people's outlook on the constitution. But makes a compelling case and he is thorough. It's more worthwhile to read it both for a deeper understanding of how Lincoln viewed his presidency (especially illuminating compared to the recent former president) and for those interested in writing itself.