I haven't read the book, of course, but synthesizing various reviews and excerpts, Comey's basic point seems to be: Everything I did, I did it for the reputation and purity of essence of the FBI, because it is extraordinarily important to pursue partisan ends in the name of nonpartisanship to the maintain the dignitude the most important institution in the history of the universe, or civilization will fall apart.
Or something.
He is... bad and stupid and the kind of guy who gets high on his own farts.