John Brown would have been using the King James Version of the Bible. At the end of his life he possessed an edition published by the American Bible Society in 1854. When he was imprisoned, following the raid on Harpers Ferry, Brown marked passages in this Bible. Before he was executed he gave it to his jailer, John H. Blessing.

Brown's followers would almost certainly have been most familiar with the King James Version. The only other Bible translation in widespread use in the early nineteenth century United States would have been the Douay–Rheims (Challoner revision), which was specifically Roman Catholic.

Many of Brown's followers had Christian backgrounds. Edwin and Barclay Coppack, for example, were raised as Quakers. Aaron Dwight Stevens' father had worked as a choir director at a Congregational church.

Not all of the raiders stayed Christian though. John Henry Kagi, Brown's second-in-command, was a freethinker and religious skeptic. Apparently before the raid he would get into religious debates with Brown. All of the 22 raiders shared a commitment to abolition, but they didn't necessarily have uniform views on religion or see the raid as religiously motivated.

Sources consulted:

DeCaro, Louis A. “Fire From the Midst of You”: A Religious Life of John Brown. New York: New York University Press, 2002, particularly pg. 11.

Oates, Stephen. To Purge This Land with Blood a Biography of John Brown. New York: Harper & Row, 1970.

Reynolds, David S. John Brown, Abolitionist: The Man Who Killed Slavery, Sparked the Civil War, and Seeded Civil Rights. New York: Vintage Books, 2005.