What is the central idea of the battle of Gettysburg

General Robert E. Lee's main purpose of the Battle of Gettysburg was to move the majority of the fight into Union territory. It was the bloodiest battle of the entire Civil War and President Lincoln wrote The Gettysburg Address centered around it. The message of the Gettysburg Address was that any war we may fight cannot compare to the war in which the first pilgrims and Americans fought to start a new country in foreign land and separate from the motherland.