Lincoln did say, at one point before 1862, that if he could preserve the Union without freeing one slave, he would. But he evolved in his perception of slavery--before the Civil War, he was endorsing ideas of sending the slaves back to Africa.

He came to realize that they had the right both to be free and to stay in the US--and that emancipation was both good politics (to keep the UK from joining the southern cause) and simple justice (yes, I know the Emancipation Proclamation freed no slaves immediately--but at that point his intention was freedom for all.)