BG Chap 18 - Those who are unqualified for this knowledge

This confidential knowledge may not be spoken to one who does not have sense control. Even if he has sense control, it should not be given to a non devotee, who has no devotion to the teacher and to Kṛṣṇa. And even if he has control of his senses and has devotion, it should not be given to one who has no desire to hear. And it should never be spoken to one who envies Kṛṣṇa, the possessor of eternal form and qualities, and who thinks the Lord has material form and qualities.