bāhya-sparśeṣv asaktātmā
vindaty ātmani yat sukham
sa brahma-yoga-yuktātmā
sukham akṣayam aśnute

Translation of Bhagavad Gita 5.21

Such a liberated person is not attracted to material sense pleasure but is always in trance, enjoying the pleasure within. In this way the self-realized person enjoys unlimited happiness, for he concentrates on the Supreme.

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

Sri Yamunacarya, a great devotee in Krishna consciousness, said:

yad-avadhi mama cetah krishna-padaravinde
nava-nava-rasa-dhamany udyatam rantum asit
tad-avadhi bata nari-sangame smaryamane
bhavati mukha-vikarah susthu nisthivanam ca

“Since I have been engaged in the transcendental loving service of Krishna, realizing ever-new pleasure in Him, whenever I think of sex pleasure I spit at the thought, and my lips curl with distaste.” A person in brahma-yoga, or Krishna consciousness, is so absorbed in the loving service of the Lord that he loses his taste for material sense pleasure altogether. The highest pleasure in terms of matter is sex pleasure. The whole world is moving under its spell, and a materialist cannot work at all without this motivation. But a person engaged in Krishna consciousness can work with greater vigor without sex pleasure, which he avoids. That is the test in spiritual realization. Spiritual realization and sex pleasure go ill together. A Krishna conscious person is not attracted to any kind of sense pleasure, due to his being a liberated soul.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

His mind is not attached (asaktatma) to the happiness of sense objects (bahya sparsesu), since he experiences in the soul (atmani) happiness from having attained paramatma. He attains that happiness permanently (aksayam), since, in constantly relishing the sweetness, he does not relish lower things.

Commentary by Sri Ramanuja of Sri Sampradaya:

5.21 He who finds happiness in the self within himself, his mind detached from external contact in the manner already mentioned, i.e., from experience of objects other than the self — such a person abandoning the contemplation on Prakrti or bodily experiences, has his mind engaged in the contemplation on Brahman i.e., the Atman. Thus he attains everlasting bliss which consists in the experience of Brahman (the self). Sri Krsna speaks of the abandonment of material pleasure as easy:

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

The reason why a person is free from delusion and has there mind fixed in transcendence is now being given by Lord Krishna. The word sparsesu means sense pleasures and those attached to them are called spharsa. But one whose mind is unattached and is withdrawn internally ceases to crave, yearn and desire for indulging in the objects of the senses. Such a person attains the sublime and serene bliss that is the nature of the atma or soul. Having attained the wonder of atma tattva or realisation of the soul one continuously identifies with the Brahman by being immersed in this consciousness and experiences never ending bliss.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

In this verse Lord Krishna again clarifies yoga or the science of the individual consciousness attaining communion with the ultimate consciousness and how this relates to equanimity of actions. Without any other desires internal or external only the person who relishes and revels in the atma or eternal soul is alone eligible for realisation of the Brahman or the spiritual substratum pervading all existence and the bliss accompanying it. The communion of the atma is the same as the communion of the Brahman for they both possess the same eternal nature and the only way this communion can be attained is through mediation of yoga and no other way.

Now begins the summary.

So it can be understood that if even by remembrance of the potencies of the Supreme Lord so much happiness can be gained then what can be said for one who devotes themselves wholeheartedly to the Supreme Lord in a concentrated manner.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

If a person is inclined to attachment to sensual pleasures they will never have the opportunity to experience the transcendental bliss of the realisation of the Brahman or the spiritual substratum pervading all existence. But a question may be raised what happiness can a person derive from life if they have introverted their senses and are averted to sense objects. Lord Krishna states the compound words sukham-aksayam meaning unlimited happiness is what such persons attains for with disconnection to the senses and objects of the senses a natural detachment arises which frees one from worldly desires allowing one to focus within on the eternal atma or eternal soul where one tastes boundless joy and experiences unlimited bliss. In the moksadharma section of the Mahabharata it states that: The pleasures of the senses in this world and the joys of heavenly pleasures cannot be compared to even 1/16th part of the pleasure one derives from renouncing the desire for material sense gratification. This is the essential component that paves the way for perceiving the Brahman or spiritual substratum pervading all existence, atma tattva or realisation of the soul and moksa or liberation from the material existence and cognition of the ultimate truth of the Supreme Being.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

5.21 Asakta-atma, with his heart, internal organ, unattached, bahya-sparsesu, to external objects-sparsah means objects that are contacted, viz sound etc.; bahya-sparsah means those things which are external (bahya) and are objects of contact; that person who thus has his heart unattached, who derives no happiness from objects; he vindati, gets that sukham, bliss; yat, which is; atmani, in the Self. Brahma-yoga-yukta-atma, with his heart absorbed in meditation on Brahman-meditation (yoga) on Brahman is brahma-yoga; one whose internal organ (atma) is absorbed in (yukta), engaged in, that meditation on Brahman is brahma-yoga-yukta-atma; he asnute, acquires; aksayam, undecaying; sukham, Bliss. So, he who cherishes undecaying happiness in the Self should withdraw the organs from the momentary happiness in external objects. This is the meaning. For this reason also one should withdraw:

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

5.21 He, in whom there is no desire for the external touch viz., the object-he thinks says as follows the Bhagawat –

Sanskrit Shloka Without Transliteration Marks:

bahya-sparsesv asaktatma
vindaty atmani yat sukham
sa brahma-yoga-yuktatma
sukham aksayam asnute

Sanskrit to English Word for Word Meanings:

bāhya-sparśeṣu — in external sense pleasure; asakta-ātmā — one who is not attached; vindati — enjoys; ātmani — in the self; yat — that which; sukham — happiness; saḥ — he; brahma-yoga — by concentration in Brahman; yukta-ātmā — self-connected; sukham — happiness; akṣayam — unlimited; aśnute — enjoys.