The answer is: To readmit the former Confederate states without imposing harsh conditions
Because of the spark of the Civil War, Lincoln's main goal was to reunify the United States. His approach to this was based on a policy of forgiveness, amnesty, and reconstruction. With this, he would find a way to rally support from the northern states and also persuading the southern states to surrender to their cause.
Many Republicans sought to implement harsh repercussions on the states that fought on the side of the Confederacy but Lincoln knew that, in order to achieve reunification he needed to be less strict and more progressive.