To bring the country (especially the North) together, when it was divided by different views of the war, to reiterate his view of the purpose of the United States and to provide a direction for the future 'soul' of the United States.
basically to tell foreign nations to stay out of the civil war. they wanted to send a message how The Union has turn the tide and the rebels will be conquered. For the Union, the civil war was not about slavery my but about making the union one whole.
