To the objection that since P.B.'s books contain teachings, he is therefore a guru whatever denials are made, his answer is: books are general, written for an anonymous mass-group whereas a guru is occupied with individual students, with named separate persons. An author's relationship with his reader is quite impersonal: the latter is quite unknown to the author, the former is never seen by the reader. But a guru meets, converses with, trains, and guides each disciple personally.
-- Notebooks Category 12: Reflections > Chapter 4: Reflections On Truth > # 60