Lincoln recognized that the mere granting of freedom from slavery would not make Blacks the social and political equals of white Americans. So emancipating them, and even allowing free Black males to serve in the Union Army, did not make them equal with whites. It only meant that they weren't slaves. Lincoln was changing his mind a bit on the relationship between Blacks and Whites. Before the war, he saw Blacks as a threat, but as the war went on he changed his view. He recognized the contributions that many Blacks were making, especially those who became Union soldiers.
In 1858, when he was campaigning to be Senator from Illinois, he had to be careful not to arouse the opposition of voters by seeming to support equality of any kind between White and Black Americans. Most White Americans in the North, while they may not have supported slavery, did not consider Blacks to be equals of Whites. In 1862, when he was president during a war that the North seemed unable to win, he felt that a proclamation freeing the slaves would be a good idea for many reasons. The most important reason was to “dissuade” France and England from helping the South. Both of those countries were opposed to slavery, so that Lincoln didn't think that they would support the South in preference to the North if the North appeared to abandon slavery.
Of course, in fact, the Emancipation Proclamation only applied to the states in rebellion, and wasn't