According to Chapter 18, should a Guru's instructions be kept secret? Please explain.

No, Chapter 18 argues strongly against keeping a Guru's teachings secret. The text dismisses this idea as a 'meaningless fuss' and 'merely imaginary'. It asserts that instructions, even those received in dreams, should be shared with all for their enlightenment. To support this, Chapter 18 provides the sage Budhakaushika as proof, noting that he narrated his dream-vision of the Ram Raksha initiation to everyone. The chapter's stance is that knowledge from the Guru is meant to be shared, like rain from the clouds, for the benefit of all.