So I went over to Reverend Barber's website

[DBoon]

55. The abolition of slavery was also often based on religious grounds

http://www.christianitytoday.com/history/issues/issue-33/abolitionists.html

Not that all abolitionists were orthodox Christians, though a large proportion were. But even those who had left the church drew on unmistakably Christian premises, especially on one crucial point: slavery was sin. Sin could not be solved by political compromise or sociological reform, abolitionists maintained. It required repentance; otherwise America would be punished by God. This unpopular message rankled an America that was pushing west, full of self-important virtue as God’s darling.

and http://nationalhumanitiescenter.org/tserve/nineteen/nkeyinfo/amabrel.htm:

...evangelical Christians were most especially influential when pressing their moral issues forward into the public arena. Growing out of the Great Awakening, these Protestants, largely in New England, were inspired less by earlier Calvinistic doom and gloom theology than by concepts of human betterment under God’s grace and His gift of free will. Out of this fresh religious doctrine, called Arminianism, grew a movement that included the plea for the freedom of all of God’s human creatures, especially the Southern slaves. Eventually the antislavery cause with its strong religious support helped to create the Republican party in the 1850s. This development led directly into the sectional crisis of 1860 and the war that followed.