Near as I can tell, Lincoln was a troubled skeptic with a tendency towards deism and a political pragmatist. He can be seen tempering his speech in some of his letters and in his debates with Stephen Douglas. But if you look at what he did, and the majority of his opinions across many other speeches and letter, the man clearly hated slavery; but thought that his chief concern as President clearly was the preservation of the Union first and foremost. That being said, what was the primary reasons for the Confederacy to secede from the Union? There is no debate that it was slavery, everything boils down to it; the entire 'states rights' argument rests it's foundation upon the desire to keep slavery regardless of what legislation the Federal Government passed.
"My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone I would also do that. What I do about slavery, and the colored race, I do because I believe it helps to save the Union; and what I forbear, I forbear because I do not believe it would help to save the Union. I shall do less whenever I shall believe what I am doing hurts the cause, and I shall do more whenever I shall believe doing more will help the cause."
-The Collected Works of Abraham Lincoln edited by Roy P. Basler, Volume V, "Letter to Horace Greeley" (August 22, 1862), p. 388.
"My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone I would also do that. What I do about slavery, and the colored race, I do because I believe it helps to save the Union; and what I forbear, I forbear because I do not believe it would help to save the Union. I shall do less whenever I shall believe what I am doing hurts the cause, and I shall do more whenever I shall believe doing more will help the cause."
-The Collected Works of Abraham Lincoln edited by Roy P. Basler, Volume V, "Letter to Horace Greeley" (August 22, 1862), p. 388.