I was surprised again by how Lincoln was uncomfortable speaking extemporaneously. One of his friends even used the word "frightened." He often didn't do very well at it. On his trip from Springfield to Washington he apologized over and over again that he had misspoken or said something he shouldn't have.Go see.
He spoke a little more than 100 times as President and most of these were brief remarks and responses. He spoke very few times compared to any twentieth century or twenty-first century president.
In listening to Lincoln's speeches you can hear an evolution. The First Inaugural is an attempt of a lawyer to convince people by rational argument with an appeal to the Constitution. [...] At Gettysburg and in the Second Inaugural he moves to the dimension of persuasion that is rooted in a much deeper kind of emotive way of speaking.
Lincoln as speaker
This very interesting interview with author Ronald White contains a lot of surprises: