In plain words
This teaching should never be spoken to one without tapas, one who is not a bhakta, one who does not render service, or one who finds fault with Me.
Word for word
This is never to be spoken for you to one without tapas, nor to one without devotion, nor to one who does not serve, nor to him who finds fault with Me.
The commentators
Bhagavadgītābhāṣyam
सर्वं गीताशास्त्रार्थमुपसंहृत्य अस्मिन्नध्याये, विशेषतश्च अन्ते, इह शास्त्रार्थदार्ढ्याय सङ्क्षेपतः उपसंहारं कृत्वा, अथ इदानीं शास्त्रसम्प्रदायविधिमाह —
इदं शास्त्रं ते तव हिताय मया उक्तं संसारविच्छित्तये अतपस्काय तपोरहिताय न वाच्यम् इति व्यवहितेन सम्बध्यते । तपस्विनेऽपि अभक्ताय गुरौ देवे च भक्तिरहिताय कदाचन कस्याञ्चिदपि अवस्थायां न वाच्यम् । भक्तः तपस्वी अपि सन् अशुश्रूषुः यो भवति तस्मै अपि न वाच्यम् । न च यो मां वासुदेवं प्राकृतं मनुष्यं मत्वा अभ्यसूयति आत्मप्रशंसादिदोषाध्यारोपणेन ईश्वरत्वं मम अजानन् न सहते, असावपि अयोग्यः, तस्मै अपि न वाच्यम् । भगवति अनसूयायुक्ताय तपस्विने भक्ताय शुश्रूषवे वाच्यं शास्त्रम् इति सामर्थ्यात् गम्यते । तत्र ‘मेधाविने तपस्विने वा’(यास्क. नि. २ । १ । ६) इति अनयोः विकल्पदर्शनात् शुश्रूषाभक्तियुक्ताय तपस्विने तद्युक्ताय मेधाविने वा वाच्यम् । शुश्रूषाभक्तिवियुक्ताय न तपस्विने नापि मेधाविने वाच्यम् । भगवति असूयायुक्ताय समस्तगुणवतेऽपि न वाच्यम् । गुरुशुश्रूषाभक्तिमते च वाच्यम् इत्येषः शास्त्रसम्प्रदायविधिः ॥ ६७ ॥
In plain words
The whole purport of the Gītā has been gathered up in this chapter, and most of all in its closing lines. Here, so that the meaning of the teaching should stand firm, he has drawn it together once more in a few words. And now he states the rule for how this teaching is to be handed on:
This teaching, given by Me for your good — to cut the very root of transmigration — is not for someone without discipline, without any real austerity; that restriction, though it comes earlier in the verse, belongs together with everything that follows. Even a disciplined person isn't ready for it if they have no devotion toward their teacher and toward God — not ever, not under any circumstance. And even someone devoted and disciplined isn't ready if they have no real wish to serve. Nor is it for someone who takes Me, Vāsudeva, for an ordinary man and resents Me, accusing Me of vanity or worse, unable to bear the truth of who I actually am — that person, too, is simply not fit to hear it. What follows from all this, put positively: it belongs to someone free of envy toward the Lord, disciplined, devoted, and eager to serve. And tradition adds a further nuance — either genuine intelligence or genuine austerity will do, so long as it comes paired with real service and devotion; without that pairing, neither sharp intellect nor rigorous discipline alone is enough. And even someone who seems to have every other virtue is disqualified the moment envy toward the Lord creeps in. In the end, it belongs to whoever truly serves their teacher and holds real devotion. This, simply, is how this teaching is meant to be passed on.
Close to the Sanskrit
Having drawn together the entire purport of the Gītā-teaching in this chapter, and especially at its end — here, for the firmness of the meaning of the teaching, having made the conclusion in brief — then, now, he states the rule of the handing-down of the teaching:
This teaching, spoken by me for your benefit — for the cutting off of transmigration — is not to be told to one without austerity, one devoid of austerity: thus [this negation], though placed apart [in the sentence], is [properly] construed [with what follows]. Even to an ascetic, if devoid of devotion toward the teacher and the Deity, it is not to be told at any time, in any circumstance whatsoever. To one who, though devoted and possessing austerity, is not desirous of serving [the teacher], to him too it is not to be told. Nor, moreover, [is it to be told] to one who, taking me, Vāsudeva, to be an ordinary human being, resents [Me] by imputing faults such as self-praise, not knowing my status as truly the Lord, and cannot bear [the truth of it] — he too is unfit; to him too it is not to be told. It is understood, from the force [of these negations], that the teaching is to be told to one endowed with freedom from envious fault-finding toward the Lord, possessing austerity, devoted, and desirous of serving. There, from the indication of an alternative between these two — 'to the intelligent, or to the ascetic' (Yāska's Nirukta 2.1.6) — [it follows that] it is to be told to one possessing austerity together with the wish to serve and devotion, or likewise to one intelligent together with that same [wish to serve and devotion]. To one devoid of the wish to serve and devotion, it is not to be told, neither to the ascetic nor to the intelligent. Even to one possessing every [other] quality, if endowed with envious fault-finding toward the Lord, it is not to be told. And it is to be told to one possessing service to the teacher and devotion — this is the very rule for the transmission of the teaching.