Things that have struck me before in reading Lincoln's statements, and struck me again now:
Lincoln was a lawyer, who valued a clear line of argumentation- evidence, warrant, conclusion, all that- and who appreciated the power of words. He could be long-winded and unnecessarily thorough, but the force of his thought was always very clear.
Lincoln was a master of what we would today call "PR" and "spin." He very precisely modulated his public image and messages, saying no more or less than he wanted to say- which could be more or less than he meant. He was a master of ambiguity, and knew that his audience would read into his remarks what they wanted to hear, if he left them room to do so; and he exploited this to maintain control of his party and of public and international opinion.
But he did so while remaining essentially honest. With Fort Sumter, he honorably maintained his obligations as he saw (or construed) them, while letting the rebels make the first overtly aggressive act. With the Emancipation Proclamation, he carefully laid the ground for his new policy by publicly seeming to equivocate about it, leaving presidential emancipation on the table, expressing doubts about it, while never disavowing it. As much as he was a moral man, Abraham Lincoln was a man who was very talented at seeming to be moral, and to represent moral causes.
Is this itself immoral? Should he not rather have merely striven to be moral, and let people think of that what they will? It's certainly frustrating; but this ability to mold public perceptions and turn oneself (or allow oneself to be turned) into a figurehead for a cause is, I think, itself essentially amoral, and actually necessary for a good politician in a democratic system. It's definitely a characteristic of America's greatest presidents- Washington and both Roosevelts, for example. It really comes down to the ends to which these means are applied- many tyrants and dictators have had similar talents, but applied them to infinitely more malicious ends.
The mismatch between what Lincoln thought, what he intended to do, what he said he was going to do, and what he actually did, must've made him very frustrating to work with at times, but he was also a master at using diplomacy, humor, and restraint to win over the goodwill of his colleagues and subordinates. I'm not sure he could've maintained the balancing act he was engaged in much longer, had he lived- it was hard enough to hold the Radicals, moderates, and conservatives in his party in a state of equilibrium during the war, and the situation only became more fraught and difficult during Reconstruction.
Lincoln was a man who framed his most radical acts in terms of maintaining or realizing the ideals of honored forebears. His arrogation of power to the federal government (and the executive in particular), and his moves to end slavery, were the most radical things a 19th century president ever did; yet he tended to cast them as sensible, conservative acts, necessary to preserve and burnish the Union handed down to him by his forebears. He was certainly right about the latter part, but maybe not about the former.