yadā viniyataḿ cittam
ātmany evāvatiṣṭhate
nispṛhaḥ sarva-kāmebhyo
yukta ity ucyate tadā

Translation of Bhagavad Gita 6.18

When the yogi, by practice of yoga, disciplines his mental activities and becomes situated in transcendence—devoid of all material desires—he is said to be well established in yoga.

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

The activities of the yogi are distinguished from those of an ordinary person by his characteristic cessation from all kinds of material desires—of which sex is the chief. A perfect yogi is so well disciplined in the activities of the mind that he can no longer be disturbed by any kind of material desire. This perfectional stage can automatically be attained by persons in Krishna consciousness, as stated in the Srimad-Bhagavatam (9.4.18–20):

sa vai manah krishna-padaravindayor
vacamsi vaikuntha-gunanuvarnane
karau harer mandira-marjanadisu
shrutim cakaracyuta-sat-kathodaye 

mukunda-lingalaya-darsane drsau
tad-bhritya-gatra-sparse ’nga-sangamam
ghranam ca tat-pada-saroja-saurabhe
srimat-tulasya rasanam tad-arpite 

padau hareh kshetra-padanusarpane
siro hrishikesha-padabhivandane
kamam ca dasye na tu kama-kamyaya
yathottama-sloka-janasraya ratih

“King Ambarisha first of all engaged his mind on the lotus feet of Lord Krishna; then, one after another, he engaged his words in describing the transcendental qualities of the Lord, his hands in mopping the temple of the Lord, his ears in hearing of the activities of the Lord, his eyes in seeing the transcendental forms of the Lord, his body in touching the bodies of the devotees, his sense of smell in smelling the scents of the lotus flowers offered to the Lord, his tongue in tasting the tulasi leaf offered at the lotus feet of the Lord, his legs in going to places of pilgrimage and the temple of the Lord, his head in offering obeisances unto the Lord, and his desires in executing the mission of the Lord. All these transcendental activities are quite befitting a pure devotee.”

This transcendental stage may be inexpressible subjectively by the followers of the impersonalist path, but it becomes very easy and practical for a person in Krishna consciousness, as is apparent in the above description of the engagements of Maharaja Ambarisha. Unless the mind is fixed on the lotus feet of the Lord by constant remembrance, such transcendental engagements are not practical. In the devotional service of the Lord, therefore, these prescribed activities are called arcana, or engaging all the senses in the service of the Lord. The senses and the mind require engagements. Simple abnegation is not practical. Therefore, for people in general—especially those who are not in the renounced order of life—transcendental engagement of the senses and the mind as described above is the perfect process for transcendental achievement, which is called yukta in the Bhagavad-gita.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

When does the yogi perfect that yoga? This verse describes that situation. The consciousness stops all movement (viniyatam cittam), and is firmly fixed without distraction in the self alone (atmani avatisthate).

Commentary by Sri Ramanuja of Sri Sampradaya:

6.18 When the mind which usually goes after sense enjoyments, abandons such desires and ‘rests on the self alone,’ i.e., becomes well-settled on account of discerning unsurpassable good in the self alone and rests there alone steadily, without movement — then, being ‘free of yearning for all desires,’ one is said to be integrated. He is said to be fit for Yoga.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

When does a person perfect the practise of yoga or the science of the individual consciousness attaining communion with the ultimate consciousness? The answer is when the mind becomes fixed and focused exclusively on the atma or soul within. Lord Krishna declares that at this time a person can be considered as having perfected yoga.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

The word atmany is used by Lord Krishna to indicate the eternal transcendental abode of the Supreme Lord.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

When will the persons qualified to practice yoga or the science of the individual consciousness attaining communion with then ultimate consciousness become established in yoga reaching perfection. Lord Krishna declares that when the mind refrains and abstains from all external mental activity and becomes exclusively riveted internally on the atma or soul within. Then it has been determined by experts that the mind is established in yoga.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

6.18 A yogi, nihsprhah, who has become free from hankering, thirst; sarva-kamebhyah, for all desirable objects, seen and unseen; is tada, then; ucyate, said to be; yuktah, Self-absorbed; yada, when; the viniyatam, controlled; cittam, mind, the mind that has been made fully one-pointed by giving up thought of external objects; avatisthate, rests; atmani eva, in the non-dual Self alone, i.e. he gets established in his own Self. An illustration in being given for the mind of that yogi which has become Self-absorbed:

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

6.18 Yada etc. The distinguishing mark of this man of Yoga is : Havnig his mind controlled in nothing but the Self, he does not crave at all [for anything].

Sanskrit Shloka Without Transliteration Marks:

yada viniyatam cittam
atmany evavatisthate
nisprhah sarva-kamebhyo
yukta ity ucyate tada

Sanskrit to English Word for Word Meanings:

yadā — when; viniyatam — particularly disciplined; cittam — the mind and its activities; ātmani — in the transcendence; eva — certainly; avatiṣṭhate — becomes situated; nispṛhaḥ — devoid of desire; sarva — for all kinds of; kāmebhyaḥ — material sense gratification; yuktaḥ — well situated in yoga; iti — thus; ucyate — is said to be; tadā — at that time.