John Brown's willingness to die took him from being a madman to being a martyr; made him sane, not insane.

    The text (in blue below) is from Samuel C. Gwynne's book Rebel Yell: The Violence, Passion, and Redemption of Stonewall Jackson, showing how John Brown went from being a madman to a martyr and how delusion took root in Virginia and in rest of the South.  Brown's death made the division of the nation a reality in the minds of the people.

"What happened in the weeks and months after Brown’s trial and execution amounted to an almost instant revision of history, changing entirely the meaning of his raid in the minds of everyone in slave and non-slave America.

"The first perception of Brown and his attack on Harpers Ferry were easily categorized: he may have thought he was working to abolish slavery, but in fact he was delusional, perhaps even insane.

"It followed that Brown and his cohorts were only a tiny splinter group of radicals and did not represent the way most abolitionists in the North actually felt. This certainly was the quickly expressed view in the North.

"The antislavery Worcester Spy, in Massachusetts, called it “one of the rashest and maddest enterprises ever.” Arch-abolitionist William Lloyd Garrison thought that, though it might have been “well intended,” it was also “misguided, wild, and apparently insane.”  

"But at his trial Brown surprised everyone. He was not only coolly rational but also remarkably eloquent.

“I deny everything but what I have all along admitted,” he said, “of a design on my part to free the slaves. Had I interfered in the manner which I admit in behalf of the rich, the powerful, the intelligent, the so-called great, every man in this Court would have deemed it an act worthy of reward rather than punishment.

"This Court acknowledges, too, the validity of the law of God. I see a book kissed, which I suppose to be the Bible, or at least the New Testament, which teaches me that all things whatsoever that men should do to me, I should do so even to them.

"Now, if it is deemed necessary that I should forfeit my life for the furtherance of the ends of justice and mingle my blood further with the blood of my children and with the blood of millions in this slave country whose rights are disregarded by wicked, cruel, and unjust enactments. I say, let it be done.' 

Brown’s words and his self-possession in the courtroom—changed everything. These were not the words of a madman and a murderer, as Northerners now saw it, but of a principled religious man who insisted that his purpose had not been to incite rebellion but simply to arm slaves for their self-defense. The change of perception swept quickly through the nonslave states in the days following the trial.

The day he was executed, church bells tolled in many Northern towns and cities; guns fired salutes; sermons were preached on the purity and correctness of his motives; and people all over the North prayed for the soul of this martyr to liberty. Brown’s death was no longer an oddity.

It was suddenly a sensation. Henry David Thoreau called him a “crucified hero.” William Dean Howells, a leading Northern intellectual, wrote that Brown has "become an idea, a thousand times purer and better and loftier than the Republican idea.” Everyone was suddenly talking about the grandeur and nobility of the man, the rightness of what he had done.  

The reaction of Southerners to such Northern expressions of sympathy was horror mixed with disbelief that their brethren could possibly wish upon them the fate that Brown had planned.

To Southerners and particularly Virginians, whose state had been invaded, Brown was a terrifying figure, the dark, avenging side of the antislavery movement that had been on view for five years in the bloody civil war in Kansas—where Brown and his Free State volunteers had murdered five men in 1856.

He had, after all, intended to arm slaves and set them free, which presumably meant setting them upon their masters, which meant that people in Connecticut and Massachusetts were now endorsing the violent deaths of white men, women, and children all over the South.

“This mad attempt by a handful of vulgar cutthroats and its condign punishment,” wrote the Reverend Robert Lewis Dabney, an important Presbyterian leader in the South and later chief of Jackson’s staff, “would have been a very trivial affair to the Southern people, but for the manner in which it was regarded by the people of the North.

"Their presses, pulpits, public meetings and conversations, disclosed such a hatred of the South and its institutions, as to lead them to justify the crime, involving though it did the most aggravated robbery, treason and murder; [and] to exalt the bloodthirsty fanatic who led the party, to a public apotheosis.”

-- Rebel Yell: The Violence, Passion, and Redemption of Stonewall Jacksonf
Samuel C. Gwynne pages 25-26