A spiritual teacher (outside of yourself) might considered it a threat if him/her followers listen to their own inner guidance (the real Guru) over the teacher's guidance.

I had to look up the word threat because I couldn’t see where the questioner was coming from. I found the Cambridge dictionary definition (see number 3 below), to give me a clue asking : will something unpleasant happen to follow “all others merely show the way”, thinking that Nisargadatta is warning to follow only the Real guru. The pointing of the way is not the Real guru but is very helpful and i was personally grateful to my teachers for their consistent pointers to Truth. Doreen’s point highlighted that not all teachers are focused on Truth .

Threat ( from google search)

• a statement of an intention to inflict pain, injury, damage, or other hostile action on someone in retribution for something done or not done.
• "members of her family have received death threats"

• ◦

• a person or thing likely to cause damage or danger.
• "hurricane damage poses a major threat to many coastal communities"
• Cambridge dictionary definition :a suggestion that something unpleasant or violent will happen, especially if a particular action or order is not followed.

Thank you!