Lincoln's concern was to save the Union, not to save or destroy slavery. Lincoln would save the Union the shortest way he could under the Constitution and by using extra constitutional means.
Many people believed that the Civil War was fought on the basis of morals and ethics rather than keeping the Union intact. In truth, Lincoln waged war on secession and nation slavery, his first priority was saving the United States of America. Abraham Lincoln said "what I do about slavery and the colored race, I do because I believe it helps to save this Union" (Voices of America, p. 138). On January 1, 1863, Lincoln issued the Emancipation Proclamation where he freed all slaves in the rebellious states. Lincoln knew this would play a heavy psychological and economical toll on the South, all of which would be an advantage for the Union. Lincoln showed great determination on not allowing secession to occur, the controversial issue of slavery would not stand in the way.
Lincoln would save the Union at any cost, towards slavery. In August, 1862 Lincoln wrote a letter to Horace Greeley, an editor of the New York Tribune, who published an open letter insisting President Lincoln free the slaves immediately. In Lincoln's reply he wrote "If I could save the Union without freeing any slaves, I would do it, and if I could save it by freeing all the slaves, I would do it, and if I could do it by freeing some and leaving others alone, I would also so that" (Voices of America, p.138). Lincoln objective was to save the Union, not to either save or destroy slavery.
Lincoln's letter regarding the Union and slavery basically stated that he believed that the Union could be saved without destroying slavery. Lincoln believed if what he was doing hurts the cause he would do less and if it helped the cause he would do more. As soon as Lincoln discovered an error, he tried to correct it as soon as possible and he adopted new views as fast as they appeared to be true.
Even though his main priority was to save the Union, he had to put fourth something to calm the northern anti-slavery forces. Lincoln used his constitutional powers to issue the Emancipation Proclamation that freed the slaves in the rebellious states. He did not issue it on the border states which were still part of the Union but had slaves. He did this to keep the border states from succeeding from the Union. The border states were very important assets to the success of winning the war do to their location and population. Lincoln also suspended the habeas corpus. By doing this, he defied a ruling by the chief justice that stated that only Congress could suspend the habeas corpus based on the Constitution. Lincoln did this so that anti-Unionists could be arrested and not be tried in court. Suspending the habeas corpus is an example of how Lincoln used extra constitutional powers to rescue the Union.
Lincoln suspended habeas corpus and issued the Emancipation Proclamation to re-unite the country the shortest way possible. He had to use extra constitutional powers to do this and be successful. Not concerning with slavery, he saved the Union any way he could.