The war would have been significantly different if the Confederate States of America were to win the Battle of Gettysburg, for starters there would more than likely be a severe lack of morale in the Union ranks, there would be no Emancipation Proclamation so the slaves of the rebelling states would remain bound(wouldn't change very much), no Gettysburg Address, etc. And a very pivotal one is the European nations would probably finally acknowledge the Confederate States as a new nation, and would have supplied them, possibly causing the war to go critically into the favor of the South. With that occurrence, the Confederate States would have either won the war entirely or have forced negotiations with the Union.
Hope this helps