We work not with our body, actually, but with our mind and intelligence. So if the intelligence and the mind are always engaged in the thought of the Supreme Lord, then naturally the senses are also engaged in His service. Superficially, at least, the activities of the senses remain the same, but the consciousness is changed. The Bhagavad-gītā teaches one how to absorb the mind and intelligence in the thought of the Lord. Such absorption will enable one to transfer himself to the kingdom of the Lord. If the mind is engaged in Kṛṣṇa's service, then the senses are automatically engaged in His service. This is the art, and this is also the secret of Bhagavad-gītā: total absorption in the thought of Śrī Kṛṣṇa.
(Bhagavad-Gita----introduction).

Just as materialists engage their minds in reading newspapers, magazines and so many materialistic literatures, we must transfer our reading to these literatures which are given to us by Vyāsadeva; in that way it will be possible for us to remember the Supreme Lord at the time of death. That is the only way suggested by the Lord, and He guarantees the result: "There is no doubt."
tasmāt sarveṣu kāleṣu
mām anusmara yudhya ca
mayy arpita-mano-buddhir
mām evaiṣyasy asaṁśayaḥ
"Therefore, Arjuna, you should always think of Me in the form of Kṛṣṇa and at the same time continue your prescribed duty of fighting. With your activities dedicated to Me and your mind and intelligence fixed on Me, you will attain Me without doubt."
(Bhagavad-Gita----introduction).

The senses, the mind and the intelligence are the sitting places of this lust. Through them lust covers the real knowledge of the living entity and bewilders him.
The enemy has captured different strategic positions in the body of the conditioned soul, and therefore Lord Kṛṣṇa is giving hints of those places, so that one who wants to conquer the enemy may know where he can be found. Mind is the center of all the activities of the senses, and thus when we hear about sense objects the mind generally becomes a reservoir of all ideas of sense gratification; and, as a result, the mind and the senses become the repositories of lust.
(Bhagavad-Gita----3:40----translation and purport).

If, therefore, the soul is directly engaged with the Supreme, naturally all other subordinates, namely, the intelligence, mind and senses, will be automatically engaged. In the Kaṭha Upaniṣad there is a similar passage, in which it is said that the objects of sense gratification are superior to the senses, and mind is superior to the sense objects. If, therefore, the mind is directly engaged in the service of the Lord constantly, then there is no chance that the senses will become engaged in other ways. This mental attitude has already been explained. paraṁ dṛṣṭvā nivartate. If the mind is engaged in the transcendental service of the Lord, there is no chance of its being engaged in the lower propensities. In the Kaṭha Upaniṣad the soul has been described as mahān, the great. Therefore the soul is above all-namely, the sense objects, the senses, the mind and the intelligence. Therefore, directly understanding the constitutional position of the soul is the solution of the whole problem.
(Bhagavad-Gita-----3:42----purport).

With intelligence one has to seek out the constitutional position of the soul and then engage the mind always in Kṛṣṇa consciousness. That solves the whole problem. A neophyte spiritualist is generally advised to keep aloof from the objects of the senses. But aside from that, one has to strengthen the mind by use of intelligence. If by intelligence one engages one's mind in Kṛṣṇa consciousness, by complete surrender unto the Supreme Personality of Godhead, then, automatically, the mind becomes stronger, and even though the senses are very strong, like serpents, they will be no more effective than serpents with broken fangs. But even though the soul is the master of intelligence and mind, and the senses also, still, unless it is strengthened by association with Kṛṣṇa in Kṛṣṇa consciousness, there is every chance of falling down due to the agitated mind.
(Bhagavad-Gita-----3:42----purport).

Thus knowing oneself to be transcendental to the material senses, mind and intelligence, O mighty-armed Arjuna, one should steady the mind by deliberate spiritual intelligence (Kṛṣṇa consciousness) and thus—by spiritual strength-conquer this insatiable enemy known as lust.
This Third Chapter of the Bhagavad-gītā is conclusively directive to Kṛṣṇa consciousness by knowing oneself as the eternal servitor of the Supreme Personality of Godhead, without considering impersonal voidness the ultimate end. In the material existence of life, one is certainly influenced by propensities for lust and desire for dominating the resources of material nature. Desire for overlording and for sense gratification is the greatest enemy of the conditioned soul; but by the strength of Kṛṣṇa consciousness, one can control the material senses, themind and the intelligence. One may not give up work and prescribed duties all of a sudden; but by gradually developing Kṛṣṇa consciousness, one can be situated in a transcendental position without being influenced by the material senses and the mind—by steady intelligence directed toward one's pure identity.
(Bhagavad-Gita----3:43----translation and purport).

Such a man of understanding acts with mind and intelligence perfectly controlled, gives up all sense of proprietorship over his possessions, and acts only for the bare necessities of life. Thus working, he is not affected by sinful reactions.
A Kṛṣṇa conscious person does not expect good or bad results in his activities. His mind and intelligence are fully controlled. He knows that because he is part and parcel of the Supreme, the part played by him, as a part and parcel of the whole, is not his own activity but is only being done through him by the Supreme. When the hand moves, it does not move out of its own accord, but by the endeavor of the whole body. A Kṛṣṇa conscious person is always dovetailed with the supreme desire, for he has no desire for personal sense gratification.
(Bhagavad-Gita----4:21----translation and purport).

By practice of yoga one becomes gradually detached from material concepts. This is the primary characteristic of the yoga principle. And after this, one becomes situated in trance, or samādhi, which means that the yogī realizes the Supersoul through transcendental mind and intelligence, without any of the misgivings of identifying the self with the Superself. Yoga practice is more or less based on the principles of the Patañjali system. Some unauthorized commentators try to identify the individual soul with the Supersoul, and the monists think this to be liberation, but they do not understand the real purpose of the Patañjali system of yoga.
(Bhagavad-Gita-----6:20-23----purport).

The Supreme Lord, Kṛṣṇa, is the only controller, and all living entities are controlled by Him. These living entities are His superior energy because the quality of their existence is one and the same with the Supreme, but they are never equal to the Lord in quantity of power. While exploiting the gross and subtle inferior energy (matter), the superior energy (the living entity) forgets his real spiritual mind and intelligence. This forgetfulness is due to the influence of matter upon the living entity. But when the living entity becomes free from the influence of the illusory material energy, he attains the stage called mukti, or liberation. The false ego, under the influence of material illusion, thinks, "I am matter, and material acquisitions are mine." His actual position is realized when he is liberated from all material ideas, including the conception of his becoming one in all respects with God.
(Bhagavad-Gita-----7:5----purport).

Therefore, Arjuna, you should always think of Me in the form of Kṛṣṇa and at the same time carry out your prescribed duty of fighting. With your activities dedicated to Me and your mind and intelligence fixed on Me, you will attain Me without doubt.
This instruction to Arjuna is very important for all men engaged in material activities. The Lord does not say that one should give up his prescribed duties or engagements. One can continue them and at the same time think of Kṛṣṇa by chanting Hare Kṛṣṇa. This will free one from material contamination and engage the mind and intelligence in Kṛṣṇa. By chanting Kṛṣṇa's names, one will be transferred to the supreme planet, Kṛṣṇaloka, without a doubt.
(Bhagavad-Gita----8:7----translation and purport).

One who is not envious but is a kind friend to all living entities, who does not think himself a proprietor and is free from false ego, who is equal in both happiness and distress, who is tolerant, always satisfied, self-controlled, and engaged in devotional service with determination, his mind and intelligence fixed on Me—such a devotee of Mine is very dear to Me.
Coming again to the point of pure devotional service, the Lord is describing the transcendental qualifications of a pure devotee in these two verses. A pure devotee is never disturbed in any circumstances. Nor is he envious of anyone. Nor does a devotee become his enemy's enemy; he thinks, "This person is acting as my enemy due to my own past misdeeds. So it is better to suffer than to protest."
(Bhagavad-Gita----12:13-14----translation and purport).

He is tolerant, and he is satisfied with whatever comes by the grace of the Supreme Lord. He does not endeavor much to achieve something with great difficulty; therefore he is always joyful. He is a completely perfect mystic because he is fixed in the instructions received from the spiritual master, and because his senses are controlled he is determined. He is not swayed by false arguments, because no one can lead him from the fixed determination of devotional service. He is fully conscious that Kṛṣṇa is the eternal Lord, so no one can disturb him. All these qualifications enable him to fix his mind and intelligence entirely on the Supreme Lord. Such a standard of devotional service is undoubtedly very rare, but a devotee becomes situated in that stage by following the regulative principles of devotional service. Furthermore, the Lord says that such a devotee is very dear to Him, for the Lord is always pleased with all his activities in full Kṛṣṇa consciousness.
(Bhagavad-Gita-----12:13-14----purport).