Bhagavad Gita Verse 67, Chapter 18

idam te naatapskaaya naaabhaktaaya kadaachana |
na chaashushrooshave vaachyam na cha maam yobhyasooyati || 67 ||
 
This what has been taught to you, should never be taught to one without penance, one who is not a devotee, one without service, and to one who has an objection to me.
 
idam : this
te : you
na : not
atapskaaya : one without penance
na : not
abhaktaaya : one who is not a devotee
kadaachana : never
na : not
cha : and
ashushrooshave: one without service
vaachyam : taught
na : not
cha : and
maam : my
yaha : who
abhyasooyati : objects
 
In India, scriptural knowledge has always been handed down from the teacher to the student. There are rules with regards to how a teacher should be selected, how a student should be selected, what the teaching method should look like. We cannot read a serious text like we read a magazine or a newspaper, nor can we expect an undergraduate student of arts to solve a PhD level differential equation. Therefore, a serious study of the Gita should also follow certain guidelines and rules. Here, Shri Krishna enumerates these rules.
 
The Gita should not be taught to one who has not undergone a certain degree of penance or austerity. He should be willing to bear some physical discomfort while attending a discourse, for instance. It is clear that one who wants to visit the bar every night and follow it with a visit to the club will not gain any benefit from the Gita. A certain level of detachment from the material world is required. Secondly, the Gita should not be taught to someone who is not a devotee. If the student does not harbour respect for the guru, the teacher, he does not have the requisite level of humility to undertake spiritual inquiry.
 
The word shushrushaa has two meanings. It refers to one who has an attitude of service towards the world, instead of a highly selfish outlook. It also refers to one who is fond of listening to discourses. The Gita should not be taught to one who is highly selfish, nor to one who is not interested in listening to any kind of discourse. Finally, the Gita should not be taught to anyone who has objection to the notion that there is Ishvara, there is something beyond the material world. The Gita is not meant for purely materialistic individuals who are content with their existence.