God i hated that part.
The book easily explained the power of the Fremen in a simple scene when Thufir Hawat talks with Baron Harkonnen about them.
Fremen grow up in one of the harshest environment known to mankind where they have to fight for their life each day and they manage to thrive in that environment. That's it.. simple but a really powerful explanation.
I never understood why Lynch never used this explanation.
I have the second and third books, and just as soon as I finish 'World War Z' I intend to read them.
After you read them you should also read God Emperor, Heretics and Chapterhouse too. God Emperor was weird when I read it for the first time, I almost gave up, don't make that mistake, it's incredible. Heretics and Chapterhouse are great too and unlike many others I don't mind the ending.
Don't bother with the prequels, sequels and interquels written by Brian Herbert and kevin J. Anderson, they're so inferior it's not even funny. The Prelude to Dune trilogy has some nice moments but it feels like an alternate universe and the story could have been told in one novel, it didn't have to be a trilogy.
The Legnds of Dune trilogy takes the legend of the Buthlerian Jihad and turns it into nothing but a set-up for Brian Herbert's sequel to Chapterhouse, a shitty ending that really doesn't feel like it's ending the story Frank Herbert started.
They had pretty much admitted they had no idea what Herbert had planned. The two thinking machines as the final villains was the best those hacks could do. Whatever ideas Herbert really had, he took to the grave sadly.