Earlier quoted context omitted.
It's remarkable if we can observe these differences directly given our currently rather course scanning mechanisms. That may or may not be what the author was saying though.
Not to nit-pick, intended to help: I think you mean "coarse" rather than "course". After the item here a day or two ago about Garden Path sentences, your comment took me several re-takes to parse correctly.
To me it seemed easy to understand: I think the internal process is that as I read I'm speaking internally to myself and so hear¹ the phonic reproduction, homophones don't matter then, the meaning is clear as in that context "rather course" the path/progression/learning-period meaning of course is nonsensical. Also there's probably something in the couplet "rather coarse" being common and there being few words that can follow rather.
I'm pretty good at proof reading but making many homophone (homophonic?) errors in informal writing.
--- ¹ I wrote this as "here", lol.