Bhagavad Gita Chapter 18 Verse 67
भगवद् गीता अध्याय 18 श्लोक 67

इदं ते नातपस्काय नाभक्ताय कदाचन।
न चाशुश्रूषवे वाच्यं न च मां योऽभ्यसूयति।।18.67।।



English Translation - Swami Sivananda
18.67 This is never to be spoken by thee to one who is devoid of austerities or devotion, nor to one who does not render service or who does not desire to listen, nor to one who cavils at Me.


English Translation of Sanskrit Commentary By Sri Shankaracharya's
18.67 Idam, this Scripture; which has been taught by Me te, to you, for your good, for terminating mundane existence; an vacyam, should not be taught (-na is connected with the remote word vacyam-); atapaskaya, to one who is devoid of austerities. It should kadacana, never, under any condition whatsoever; be taught abhaktaya, to one who is not a devotee, who is devoid of devotion to his teacher and God, even if he be a man of austerity. Neither should it be taught even asurusave, to one who does not redner service-even though he may be a devotee and a man of austerity. Na ca, nor as well; to him yah, who; abhyasuyati, cavils; mam, at Me, at Vasudeva-thinking that I am an ordinary person; to him who, not knowing My Godhood, imputes self-adulation etc. to Me and cannot tolerate Me. He too is unfit; to him also it should not be imparted.
From the force of the context it is understood that the Scripture should be taught to one who has devotion to the Lord, is austere, renders service, and does not cavil. As to that, since it is seen (in a Smrti)-to one who is intelligent or to one who is austere-that there is an option between the two, it follows that this should be imparted either to an austere person given to service and devotion, or to an intelligent person endowed with them. It should not be imparted to an austere or even an intelligent person if he lacks service and devotion. It should not be taught to one who cavils at the Lord, even though he be possessed of all the good alities. And it should be taught to one whoserves his teacher and is devout. This is the rule for transmitting the Scripture.
Now the Lord states the fruit derived by one who transmits the Scripture:


Transliteration Bhagavad Gita 18.67Idam te naatapaskaaya naabhaktaaya kadaachana;
Na chaashushrooshave vaachyam na cha maam yo’bhyasooyati.


Word Meanings Bhagavad Gita 18.67idam—this; te—by you; na—never; atapaskāya—to those who are not austere; na—never; abhaktāya—to those who are not devoted; kadāchana—at any time; na—never; cha—also; aśhuśhrūṣhave—to those who are averse to listening (to spiritual topics); vāchyam—to be spoken; na—never; cha—also; mām—toward me; yaḥ—who; abhyasūyati—those who are envious