I noticed that the "Autobiography of a Yogi" is written in rather difficult and sophisticated prose. Was this because Yogananda did not intend that particular book for uneducated, lower class audiences?
That’s an excellent question. The first time or two that I read that book, I had to have a dictionary nearby—and I have a PhD! e.g., "Ineluctable quiddity"!
I am not aware of Yoganandaji having commented on why he wrote it as he wrote it. Though English was not his first language, his vocabulary was indeed large, and he may have used a great deal of it.
Then too, we don’t know exactly what he wrote, as the book was edited, and the editor had her own ideas about how to express certain points.
All I can say is that a great master would be much more concerned with conveying vibration than with grammar and vocabulary, and that book is loaded with vibration.
I have known quite a number of "uneducated" people who found great inspiration in it, even if they tripped over a number of sentences.
It seems to me that those who resonate with his vibration will understand the teachings in the book, regardless of whether those persons can decipher every last bit of it intellectually.