yato yato niścalati
manaś cañcalam asthiram
tatas tato niyamyaitad
ātmany eva vaśaḿ nayet

Translation of Bhagavad Gita 6.26

From wherever the mind wanders due to its flickering and unsteady nature, one must certainly withdraw it and bring it back under the control of the self.

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

The nature of the mind is flickering and unsteady. But a self-realized yogi has to control the mind; the mind should not control him. One who controls the mind (and therefore the senses as well) is called gosvami, or svami, and one who is controlled by the mind is called go-dasa, or the servant of the senses. A gosvami knows the standard of sense happiness. In transcendental sense happiness, the senses are engaged in the service of Hrishikesha, or the supreme owner of the senses—Krishna. Serving Krishna with purified senses is called Krishna consciousness. That is the way of bringing the senses under full control. What is more, that is the highest perfection of yoga practice.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

If the mind, contacting the mode of passion, happens to become unsteady due to the appearance of previous attachments, one should again practice yoga.

Commentary by Sri Ramanuja of Sri Sampradaya:

6.26 Wherever the mind, on account of its fickle and unsteady nature, wanders, because of its proclivity to sense-objects, he should, subduing the mind everywhere with effort, bring it under control in order to remain in the self alone by contemplating on the incomparable bliss therein.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Now Lord Krishna a specific example that if the mind losing its equilibrium begins to waver due to the influence of rajas or passion. Then the mind should be apprehended and brought securely under control guided back to focus on the atma or soul in a serene meditative state. So the conclusion is that whatever object tempts the unsteady mind to pursue it; from that very same object one must withdraw the restless mind and steady solely in the eternal atma.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

Whatever also means wherever. Wherever the mind turns to in pursuit of any external object whatever it should be diverted back and re-routed within to the atma or soul inside and exclusively installed reside there. This is Lord Krishna’s meaning.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

A question may be raised that if the controlled mind becomes suddenly tempestuous and restless what should be done? Lord Krishna answers this question here. The mind must be immediately rescued back from whatever sense object that caused the mind to deviate and this should be done again and again until the mind becomes fixed in the atma or soul.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

6.26 In the beginning, the yogi who is thus engaged in making the mind established in the Self, etat vasamnayet, should bring this (mind) under the subjugation; atmani eva, of the Self Itself; niyamya, by restraining; etat. it; tatah tatah, from all those causes whatever, viz sound etc.; yatah yatah, due to which, doe to whatever objects like sound etc.; the cancalam, restless, very restless; and therefore asthiram, unsteady; manah, mind; niscarati, wanders away, goes out due to its inherent defects. (It should be restrained) by ascertaining through discrimination those causes to be mere appearances, and with an attitude of detachment. Thus, through the power of practice of Yoga, the mind of the yogi merges in the Self Itself.

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

6.26-28 Yatah etc. upto adhigacchati. From whatever objects the mind returns, immediately after its return, let him quieten it on the Self. Otherwise, being not firmly established [in the Self], the mind would again take hold of nothing but the sense-objects. But the Bliss, assuming the roll of an agent (or subject, kartv-bhuta) comes to the object (karmabhuta), viz., the man-of-Yoga, whose mind remains quite in the Self. By this way alone the men-of-Yoga attain the Brahman easily and not by [any] difficult Yoga etc. This is the idea [here].

Sanskrit Shloka Without Transliteration Marks:

yato yato niscalati
manas cañcalam asthiram
tatas tato niyamyaitad
atmany eva vasam nayet

Sanskrit to English Word for Word Meanings:

yataḥ yataḥ — wherever; niścalati — becomes verily agitated; manaḥ — the mind; cañcalam — flickering; asthiram — unsteady; tataḥ tataḥ — from there; niyamya — regulating; etat — this; ātmani — in the Self; eva — certainly; vaśam — control; nayet — must bring under.