I read very well, but you know some stuff is just so hard to read. St. John of the Cross comes to mind with "Dark Night of the Soul" Arg!
Lewis often said that obscure language or jargon was a sure sign that you didn't thoroughly understand what you were talking about and were taking refuge in "shop talk". He recommended that anybody writing something technical (whether textual analysis or theology) put it in "plain English" before publication.
What's interesting is that his personal, plain-spoken tone is evidence even in his "day job" writings - he wrote the volume of the Oxford History of English Literature on the 16th Century (excluding drama, which had a volume of its own), and it's quite engaging, very friendly and chatty, even though the subject is obscure. I mean, who has read David Lyndsay's The Monarche lately? although if you do (or if you read Lewis' tome) you'll find out where the title of That Hideous Strength came from!