The correct answer to this open question is the following.
The Battle of Vicksburg began on May 18, 1963, and ended until July 4, 1963. Vicksburg was the major port in the Mississippi River still controlled by the Confederate Army at that time. General Ulysess Grant knew about the importance of the battle because a victory for the North represented the control of the supplies lines from the West and the isolation of southern states such as Louisiana, Texas, and Arkansas, from other states. Grant ordered the surrounding of the city and that was the path to victory.
The Battle of Gettysburg was fought from July the 1st to the 3rd, 1863, in Gettysburg, Pennsylvania. Confederate leader General Robert E. Lee was already in the north and knew that a victory in Gettysburg represented a big step to winning the war. Union's General George Meade could stop the Confederate Army during three days of bloody battle and ended up winning the battle that historians say it represented a turning point in the Civil War.
Definitely, the victory in Gettysburg represented the final boost that the Union Army needed because the Confederated Army was already in the "front door" of the northern states. With the defeat, the moral of the southern army fell down to a degree that it could be said that this loss cost them the war.