“Abraham Lincoln knew that the slaves were freed by the blood and sweat of the union soldiers.”
Slavery was not banned until the adoption of the 13th Amendment in December, 1865, after the Civil War had ended. If the North was so interested in freeing the slaves, why is it that northern states such as Delaware and New Jersey did not ratify the 13th Amendment until four years later, after having first rejected it?
pprehension seems to exist among the people of the Southern States that by the accession of a Republican Administration their property and their peace and personal security are to be endangered. There has never been any reasonable cause for such apprehension. Indeed, the most ample evidence to the contrary has all the while existed and been open to their inspection. It is found in nearly all the published speeches of him who now addresses you. I do but quote from one of those speeches when I declare that—
I have no purpose, directly or indirectly, to interfere with the institution of slavery in the States where it exists. I believe I have no lawful right to do so, and I have no inclination to do so.
During the war he had to formulate numerous policies concerning slavery and the disposition of slaves in captured territory. Rebel states were treated differently than states that remained in the union. Lincoln did not believe he had any authority over slavery in states that did not rebel. His policy towards slavery in rebel states evolved over the years of the war. Near the end of the war the union even had army units of former slaves.
McPhearson's "Battle Cry of Freedom" has a pretty good analysis of the slave problems Lincoln had to confront.