Abraham Lincoln attempted to carve out a moderate position on slavery by saying that he opposed slavery on moral grounds while also saying that he was not in favor of abolition. He particularly did not believe that the federal government had the right to end slavery. Instead, he wanted slavery to be confined to the areas where it then existed rather than allowing it to spread.
A moderate position is one that is centrist rather than extreme. One extreme position on slavery was to believe that it was a good thing and that it should be allowed in parts of the United States other than the South. Many Southerners believed this. They wanted slavery to be legal in many new territories outside the South. Lincoln certainly did not subscribe to this view.
Another extreme position on slavery was to believe that it needed to be abolished immediately, forcibly if necessary. According to this position, the government should make slavery illegal in the United States. Lincoln also did not agree with this view (most Northerners did not either). Instead, Lincoln took a view that was in between these two extreme views. He said that he personally believed that slavery was wrong. He said that he would never be willing to own a slave. He said that it would be okay with him if slavery disappeared. However, he did not say that the government should abolish it, saying instead that he did not think the US government had the right to do so under the Constitution. Here are two quotes that support this characterization of Lincoln’s views:
I think Slavery is wrong, morally, and politically. I desire that it should be no further spread in these United States, and I should not object if it should gradually terminate in the whole Union.
I say that we must not interfere with the institution of slavery in the states where it exists, because the constitution forbids it, and the general welfare does not require us to do so.