After 17 months of what had been expected to be a short war, Lincoln issued The Emancipation Proclamation and gave a 100 day grace period before it was to be effective. I remember being taught that this was a publicity stunt with no effectiveness because it only applied to states that were in rebellion. I think that is too simple a view of what Lincoln was trying to accomplish. I think it would be more accurate to say that it was a threat – with possibly a small hope that it might convince some in rebellion to end their fight against the union in order to keep their slaves before the proclamation took effect.
The goal was not to start armed rebellions within the South. In fact, what Lincoln said to those who would be freed was:
And I hereby enjoin upon the people so declared to be free to abstain from all violence, unless in necessary self-defence; and I recommend to them that, in all cases when allowed, they labor faithfully for reasonable wages.
I believe that the proclamation could be summed up as “things will be worse for rebels who refuse to come back and rejoin the nation within 100 days.” The effort was to end the war more than to free the slaves.