Abraham Lincoln did not consider himself to be an abolitionist; he did feel that slavery was morally wrong, but did not wish to change the law to eradicate it.  Abolitionists were set on changing constitutional law to end slavery and give Black people equal rights. Abraham Lincoln did not agree; he did not wish to alter the constitution.  In a court case in the 1830's, young lawyer Abraham Lincoln represented a Kentucky slave holder.  In the 1850's, Abraham Lincoln spoke about sending slaves back to Africa in a speech, theorizing that would solve the racism and issues surrounding slavery in the United States.  Abraham Lincoln did not consider himself an abolitionist and compared to true abolitionists of the time, was far from the progressive and slavery-ending President that history has painted him to be.
Abraham Lincoln was an abolitionist because he wanted to end slavery and felt slavery was morally unjust.