Why was the Battle of Antietam so important to President Lincoln

Why was the Battle of Antietam so important to President Lincoln?

How did this battle ultimately change the Civil War?
II. During the Civil War President Lincoln faced little opposition in Congress. True or False.
III. President Lincoln issued the Preliminary Emancipation Proclamation September 22, 1862. In this proclamation he made an offer to the slave states in the Union. What did he offer them?