इदं ते नातपस्काय नाभक्ताय कदाचन।न चाशुश्रूषवे वाच्यं न च मां योऽभ्यसूयति॥
idaṃ te nātapaskyāya nābhaktāya kadācanana cāśuśruṣave vācyaṃ na ca māṃ yo ‘bhyasūtayi
Word by word
The verse says
This is never to be spoken to anyone without discipline, or without love, or who will not listen, or who thinks badly of me.
In plain words
A restriction, and it is easy to read as gatekeeping. It is not quite that.
Four kinds of person: no discipline, no love, no willingness to listen, and hostility.
The common thread is not rank or learning. All four describe someone the words cannot reach, and speaking to them is not withholding. It is pointless.
Where you've felt this · in study
You try to explain something that genuinely helped you to a friend who is in a bad patch, and he is already shaking his head before you finish the first sentence. You stop. Nothing you were going to say was wrong, and none of it was going to land that evening.
Going deeper
Restrictions on teaching read badly to a modern eye, and this one is better understood as a statement about conditions than about worth.
None of the four categories is about status. Not uneducated, not low-born, not an outsider. The marks are a lack of discipline, a lack of love, an unwillingness to listen, and hostility. Any of those can describe a learned person and none of them is permanent.
The practical reading is that this material does not transfer by explanation alone. Chapter 17 said knowledge of this kind grows in the soil of what a person already is. If the soil is not ready, saying it louder does nothing, and may harden the ground.
There is also something in it for anyone who wants to be useful to people. The impulse to explain to someone who has not asked is nearly always about the explainer. Waiting until the question arrives is slower and is the only thing that works.