I did not read the parts not by Boshan. That is, the comments made by the translator, Jeff Shore, that are the last quarter of the book. I didn't read those sections - although it is possible I may return to them - because I like to read the primary text/author for myself and let his thoughts digest for awhile. I'm a wee bit more academic than most. I can't (and wouldn't) change that, however I have learned what works best for me.
Boshan's text is quite small, this isn't a huge tome. And, overall, I think the purpose is cutting away all the bulls#i₱ and fraud and deception that runs through practitioners of *any* religion due to pride, extra-independence, and laziness.
Boshan really tears into people who are playing games with Zen... or who want to partake in pop culture "zen." No one is safe - he blasts those who wrangle with koans as well as those who fanny about with the idea of being hermits.
In so doing, this becomes a very direct book. It assumes an already substantial knowledge of Zen and is more than anything, a scathing warning to those practitioners of Buddhism who are playacting. I doubt [sic] many pop culture "zen" folks will enjoy this one. The humble and the honest will be receptive to it's warnings. Maybe this thing is just a litmus test?