Why did Lincoln feel it was necessary to free the slaves?

Answer 1

Lincoln's Emancipation Proclamation was a symbolic gesture. It only freed the slaves in the states which had seceded from the union and were no longer under control of Lincoln's government. Lincoln was not a abolitionist and he had stressed the need to preserve the union as the main rationale for the War. The proclamation surely appealed to abolitionists in the North and assured them that winning the war would end slavery in the old slave states. As such it served to solidify the war effort.

There may have been hope that a slave revolt would occur in the South or that the threat of such a revolt would demoralize the South.