In my opinion, Lincoln’s single minded goal in the Civil War was the absolute destruction of slavery, which was a noble and necessary act.
I believe Lincoln put an end to slavery with none but the deepest reluctance, and then only as a means to hasten the Confederacy's defeat. He held a very low opinion of Negroes all his life, never campaigned for office or prosecuted the war as an abolitionist, and freed slaves only in the Confederacy, not the nation as a whole.
Lincoln expended a lot of effort and political capital to get slavery permanently abolished through constitutional amendment. He didn’t have to do that to merely preserve the Union.