So, after all the stuff in the first three parts contrasting intellect and emotion, and how the first can be used to manipulate the second, here we get it spelt out to us on a direct personal level by Cnaiur and Kellhus.
No wonder his tribe thought him mad. He was a man who took counsel with the dead rather than the wise
. And then he finds the spitting image of Moenghus lying on his father's grave.
Only years afterwards would he understand how those beatings had bound him to the outlander. Violence between men fostered an unaccountable intimacy... By punishing Moenghus out of desperation, Cnaiur had demonstrated need... And by demonstrating need, he'd opened his heart, had allowed the serpent to enter
. Cnaiur then gets his tribesmen to torture Kellhus, rather than getting directly involved himself - we can infer deliberately based on the quoted text.
To truly ask why, however, was to move beyond all permission.
T question everything. To ride the trackless Steppe.
"Where no paths exist, Moenghus had continued, a man strays only when he misses his destination.. There is no crime, no transgression, no sin save foolishness or incompetence, and no obscenity save the tyranny of custom...
Quite disturbing from Moenghus - anything goes. The end justifies the means. No ethics, no morals, no constraints.
Like his mother he had been seduced.
My father is dead. I was the knife.
And Anasurimbor Moenghus had wielded him.
Cnaiur realises he has been used
Triumph becomes degradation. Pride became remorse
Everything Moenghus said and did is called into question, is "taken up by the whirlwind" and re-written.
Cnaiur's wives can sense the contrast between Cnaiur (monolithic hatred) and Kellhus (godlike indifference).
Cnaiur's combination of intelligence and hate (very strong emotion?) renders Kellhus' "circumstances incalculable". He cannot be possessed, he cannot be awed, soother or flattered.
He knew too much
. Kellhus ultimately decides to kill him, once he has crossed the Steppe - but it doesn't work out that way.
We learn Kellhus can make mistakes, when he tries the 'Trackless Steppe' analogy.