How did the Gettysburg Address represent a shift in Union war goals?

In the Gettysburg Address, Abraham Lincoln fixed his attention on what kind of country the United States would be after the Civil War. It wasn't simply enough for the North to prevail in the conflict; there would need to be "a new birth of freedom" at the end of hostilities. Just as the signatories of the Declaration of Independence gave birth to a new understanding of liberty, so too must the Civil War generation reinvent the concept for the numerous challenges ahead.
The biggest challenge of all was what should be done with the four million slaves still held in bondage on American soil. In the Gettysburg Address, Lincoln radically changed Northern war aims from the preservation of the Union to the emancipation of the slaves. This was a courageous move on Lincoln's part. Most people in the North did not see the Civil War as being fought for the cause of emancipation. Indeed, many were hostile to the very idea itself, as the often fierce and bitter opposition to the Emancipation Proclamation would soon testify.
Yet Lincoln put down a marker for what kind of change he wanted to see after the war was finally over. The Gettysburg Address, aside from its inestimable value as a piece of great oratory, represented a turning point in the Civil War. Before Lincoln began his brief, yet unforgettable remarks, the war was largely a political struggle waged to save the Union from permanent dissolution. But after Lincoln finished his remarks, the whole nature of the conflict changed forever. Now the Civil War was about so much more than preserving the Republic; it was nothing less than a moral crusade.