Abraham Lincoln’s views on slavery were somewhat complex. He was, generally speaking, personally opposed to slavery, but he did not think that the government could ban slavery in the states where it already existed. Therefore, he was more of a free-soiler than an abolitionist.
There is little doubt that Lincoln personally thought slavery was an evil thing. He is quoted as having said something to the effect that he would like to try slavery out on the people who claimed it was a good thing. He believed that slavery went against the principles upon which the United States was founded.
While Lincoln thought slavery was evil, he also held views that we would now see as racist. He believed that whites were superior to blacks and that the two races could not live together as equals. For this reason, he thought that it would be better to “colonize” freed slaves to some other country rather than to keep them in the United States (this was his attitude before he was president).
Lincoln also thought that the government could not ban slavery in the South. He felt that slavery was clearly legal under the Constitution and that abolishing it would require a Constitutional amendment. He knew this would never be ratified by the South. Therefore, he was mostly concerned with preventing slavery from spreading. This was the opinion known as “free-soil” at the time.
Lincoln believed that slavery was evil. However, he did not believe that the government could legally abolish it and so he was (before the Civil War started) inclined to allow it to remain where it existed while preventing it from spreading.