nāsti buddhir ayuktasya
na cāyuktasya bhāvanā
na cābhāvayataḥ śāntir
aśāntasya kutaḥ sukham

Translation of Bhagavad Gita 2.66

One who is not connected with the Supreme [in Krishna consciousness] can have neither transcendental intelligence nor a steady mind, without which there is no possibility of peace. And how can there be any happiness without peace?

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

Unless one is in Krishna consciousness, there is no possibility of peace. So it is confirmed in the Fifth Chapter (5.29) that when one understands that Krishna is the only enjoyer of all the good results of sacrifice and penance, that He is the proprietor of all universal manifestations, and that He is the real friend of all living entities, then only can one have real peace. Therefore, if one is not in Krishna consciousness, there cannot be a final goal for the mind. Disturbance is due to want of an ultimate goal, and when one is certain that Krishna is the enjoyer, proprietor and friend of everyone and everything, then one can, with a steady mind, bring about peace. Therefore, one who is engaged without a relationship with Krishna is certainly always in distress and is without peace, however much he may make a show of peace and spiritual advancement in life. Krishna consciousness is a self-manifested peaceful condition which can be achieved only in relationship with Krishna.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

Krishna makes his statement clear by stating the effects of the opposite condition.

For one who has not controlled the mind (ayuktasya), there is no intelligence, no prajna, fixed on the soul. For one who not having such prajna arising from controlled mind, meditation on the Supreme Lord (bhavana) also is not possible. Not performing meditation (abhavayatah), he does not have peace, the cessation of agitation from sense objects. This peaceless person does not have bliss (sukham) from the soul.

Commentary by Sri Ramanuja of Sri Sampradaya:

2.66 In him who does not focus his mind on Me but is engaged only in the control of senses by his own exertion, the Buddhi or the right disposition that is concerned with the pure self never arises. Therefore he fails in the practice of meditation on the self. In one who cannot think of the pure self, there arises the desire for sense objects; in him serenity does not arise. How can eternal and unsurpassed bliss be generated in him who is not serene but is attached to sense-objects? [The idea is that without the aid of devotion to God, the effort to control the senses by one’s will power alone will end in failure.] Sri Krsna speaks again of the calamity that befalls one who does not practise the control of the senses in the way prescribed above:

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Lord Krishna now reveals the controlling of the senses as a means of attaining spiritual intelligence in a converse way. The Lord states that one with an uncontrolled mind can never possess spiritual intelligence even if well versed in the Vedic scriptures and the teachings of the bona-fide preceptor in the line of Vedic disciplic succession in one of the four authorised Vaisnava sampradaya’s. Why is this true? Because with an uncontrolled mind it is not possible to have spiritual intelligence, without spiritual intelligence one cannot meditate and without meditation it is not possible to realise the Ultimate Truth. So one who has an uncontrolled mind is bereft of this, for one who cannot meditate, who is unable to enlighten themselves within there is no peace and where there is no peace how can there be happiness.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

Lord Krishna is explaining the defects due to the absence of happiness as referred to in this verse. Without being happy there is no possibility of concentration of the mind. Without concentration of the mind there can be no meditation and without meditation it is not possible to have inner awakening or soul-cognition. Therefore it has been declared that these things are not possible for one without concentration. Santih or peace refers also to liberation. Santi, moksa or liberation and nirvana all have a similar meaning denoting termination of the samsara or worldly existence.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

In order to strengthen the previous verse Lord Krishna points out all the contrary results incurred by one with an uncontrolled mind. One who has not subdued their senses by controlling their mind is bereft of determinative resolve. The intellect of one with spiritual intelligence determines the truth ascertained in the Vedic scriptures. It is not possible for an undisciplined living entity to have belief of the calibre necessary to contemplate matters relating to the ultimate truth. Without having understanding of God there is no peace and also no end to attachment for sensual objects. How can there possibly be permanent happiness which is inexhaustible and unaffected not in the least by sorrow if one is lacking peace of mind. Although material happiness is surely derived by experiencing worldly objects, the deceptive results of this perilous interaction is very succinctly summed up subsequently in verse 38 of the final chapter of Bhagavad-Gita.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

2.66 Ayuktasya, for the unsteady, for one who does not have a concentrated mind; na asti, there is no, i.e. there does not arise; buddhih, wisdom, with regard to the nature of the Self; ca, and; there is no bhavana, meditation, earnest longing [Longing to have a continuous remembrance of the knowledge of Brahman which arises in the mind from hearing the great Upanisadic sayings (maha-vakyas).] for the knowledge of the Self; ayuktasya, for an unsteady man. And similarly, abhavayatah, for an unmeditative man, who does not ardently desire the knowledge of the Self; there is no santih, peace, restraint of the senses. Kutah, how can there be; sukham, happiness; asantasya, for one without peace? That indeed is happiness which consists in the freedom of the senses from the thirst for enjoyment of objects; not the thirst for objects — that is misery to be sure. The implication is that, so long as thirst persists, there is no possibility of even an iota of happiness! It is being stated why a man without concentration does not possess wisdom:

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

2.64-68 Raga-dvesa-etc. upto pratisthita. Here the purport is this : He, who controls his mind, is not tossed by the waves of wrath etc., even while he is enjoying the sense-objects; hence he alone is a man of Yoga, a man-of-stabilized-intellect. Extraordinary is the man of Yoga, even while he is attending to the worldly business. While examining this point, the characteristics mark of his (man of Yoga), is briefly related by the Supreme Lord-

Sanskrit Shloka Without Transliteration Marks:

nasti buddhir ayuktasya
na cayuktasya bhavana
na cabhavayatah santir
asantasya kutah sukham

Sanskrit to English Word for Word Meanings:

na asti — there cannot be; buddhiḥ — transcendental intelligence; ayuktasya — of one who is not connected (with Kṛṣṇa consciousness); na — not; ca — and; ayuktasya — of one devoid of Kṛṣṇa consciousness; bhāvanā — fixed mind (in happiness); na — not; ca — and; abhāvayataḥ — of one who is not fixed; śāntiḥ — peace; aśāntasya — of the unpeaceful; kutaḥ — where is; sukham — happiness.