What is the traditional method for acquiring spiritual knowledge from a Guru, as explained by Nana Chandorkar to Sai Baba?

According to the account in Chapter 39, Nana Chandorkar, a learned expert in Gita commentaries, explained the traditional path to acquiring spiritual knowledge. When prompted by Sai Baba, Nana recited the meaning of a verse from the Gita. He stated that one can be instructed in Knowledge by the Wise who have seen the Truth through a specific three-fold approach. This method involves prostrating at the Guru's feet, serving the Guru with one's life, and asking respectful questions. Nana emphasized that this interpretation, which highlights service and prostration as givers of Knowledge, is supported by numerous respected commentators like Shankara.