Brown was a terrorist and psychopathic, however, he did not make promises with his mouth his butt wouldn't pay on. I cannot imagine even the Antifa scum let alone the PJ boys being willing to play Alamo with half the town and county shooting at you and a the USMC on the scene looking for the fight. Most of Brown's backers were weasels except Thomas Wentworth Higginson who was a company grade officer in the 54th Mass. and saw plenty of combat. After the war Higginson became positively chummy with Jefferson Davis as he acted as the publishers editor for Davis's magnum opus ‘Rise and Fall of the Confederacy’. Go figure, Higginson was also ga ga about Thomas Nelson Page and his rather syrupy plantation novels.
Brown was a religious zealot nut, and no, he didn't want for bravery.
I have little doubt he interpreted the bible to justify his own manic impulses, but this is just him using God as a sockpuppet for his own thoughts. A lot of people do that, but fortunately not all of them are so hard core.
I think his impulses started out as hatred for his dominant competitor, but by the time he finished massaging them in his own mind, he became convinced that his adversary was evil incarnate and he was the self appointed bringer of the Lord's revenge.
It may very well be that the fear John Brown created in the South is responsible for the split. People say the Southerners acted irrationally to Lincoln's election, but it is possible that the Harper Ferry raid unnerved them, and when people are afraid, they will not always act rationally.