What was the 13th admendment? was was passing it so important to president lincoln?

Lincoln recognized that the Emancipation Proclamation would have to be followed by a constitutional amendment in order to guarantee the abolishment of slavery. The 13th amendment was passed at the end of the Civil War before the Southern states had been restored to the Union and should have easily passed the Congress.    Please give a thanks a rating and Brainlest

What are they! i have no idea lol