Easy: The Union had already freed their slaves, making the Emancipation Proclamation sort of a token gesture, but also crucially important because the South would not give up slavery so when Uncle Sam welcomed back the prodigal children he never disowned there had to be something to ensure there would be no more slaves.
What? The Union didn't free any slaves. Do you mean the North? Again, 1863 is two years later than 1861. If the War was over slavery why didn't Lincoln free them in 1861?
Plus, have you ever read the emancipation? Of course not. The emancipation didn't free one slave. Lincoln declared the slaves free 'only in Confederate held territories'. In other words Lincoln declared the ones free he couldn't free.
But, by 1863, the North had taken over quite a bit of Southern territory. And guess what, there were slaves in those territories. But Lincoln did not free them, even though he could have freed them. Only those in Confederate held territories were declared free. What a man!
In other words, Lincoln declared those free he could not free. He left those in slavery that he could have freed. Why? Slavery was just a political issue to use against the South. Slavery was never a humanitarian issue except for a few abolitionist's on the crazy fringe who were murderers. The Emancipation Proclamation was given in hopes that the slaves would rise up against the whites and slaughter them making the war effort shorter.
What do you mean 'the prodigal children he never disowned'? You live in a make believe candy land. Study the Reconstruction Amendments. The Southern states were back in and out depending on if they agreed to vote the way the North wanted them to. Then they were rejected as States and divided up into territories under martial law. They were not in the Union. They were defeated territories.
Breathe deep that smoke they blow your way. Candy land is alive and well.
Good-Ole-Rebel