B.G 5.21

बाह्यस्पर्शेष्वसक्तात्मा विन्दत्यात्मनि यत् सुखम्। स ब्रह्मयोगयुक्तात्मा सुखमक्षयमश्नुते ॥२१॥

bāhyasparśeṣvasaktātmā vindatyātmani yat sukham। sa brahmayogayuktātmā sukhamakṣayamaśnute ॥21॥

[बाह्य स्पर्शेषु असक्तात्मा विन्दति आत्मनि यत् सुखम्। स ब्रह्मयोग युक्तात्मा सुखम् अक्षयम् अश्नुते॥
bāhya = external; sparśeṣu = touch (of sense organs); asaktātmā = unattached person; vindati = experiences; ātmani = in himself; yat = which; sukham = happiness;। sa = that same; brahmayoga = by the practice of Brahma; yuktātmā = engaged being; sukham = happiness; akṣayam = everlasting / increased; aśnute = attains;]

The one who is disinterested in the external engagement of sense organs, experiences within himself happiness. The person engaging in the practice of 'Brahma-Yoga' obtains the same happiness in everlasting proportion.

Gīta Bhāshya 5.21

The remaining part of this chapter explains the combined knowledge of renunciation and Yoga. Superiority of Yōga over mere renunciation is clarified by emphasizing the undiminishing happiness one gets through Brahma-Yōga .

सन्यास योग ज्ञानानि मिलित्वा प्रपञ्चयति अध्याय शेषेण।

sanyāsa yoga jñānāni militvā prapañcayati adhyāya śeṣeṇa।

[सन्यास (sanyāsa): Renunciation or asceticism; योग (yoga): Union or discipline; ज्ञानानि (jñānāni): Knowledge; मिलित्वा (militvā): Having joined or combined; प्रपञ्चयति (prapañcayati): Propagates or spreads; अध्याय (adhyāya): Chapter or section; शेषेण (śeṣeṇa): Remaining or remaining part;]

The remaining part of this chapter explains the combined knowledge of renunciation and Yoga.

पुनः योगस्य आधिक्यं स्पष्टयति - बाह्यस्पर्शेषु इति।

punaḥ yogasya ādhikyaṁ spaṣṭayati - bāhyasparśeṣu iti।

[पुनः (punaḥ): Again or once more; योगस्य (yogasya): Of yoga; आधिक्यं (ādhikyaṁ): Superiority or predominance; स्पष्टयति (spaṣṭayati): Clarifies or explains; बाह्यस्पर्शेषु (bāhyasparśeṣu): In external sense objects; इति (iti): Thus or in this way;]

Again, the superiority of Yōga (over mere renunciation) is clarified by 'bāhyasparśeṣu' verse.

कामरहितः आत्मनि यत् सुखं विन्दति स एव ब्रह्मयोगयुक्तात्मा चेत् तदेव अक्षयं सुखं विन्दति। ब्रह्मविषयो योगः ब्रह्मयोगः। ध्यानादियुक्तस्यैव आत्मसुखम् अक्षयम्। अन्यथा नेत्यर्थः ॥२१॥

kāmarahitaḥ ātmani yat sukhaṁ vindati sa eva brahmayogayuktātmā cet tadeva akṣayaṁ sukhaṁ vindati। brahmaviṣayo yogaḥ brahmayogaḥ। dhyānādiyuktasyaiva ātmasukham akṣayam। anyathā netyarthaḥ ॥21॥

[कामरहितः (kāmarahitaḥ): Free from desire; आत्मनि (ātmani): In oneself; यत् (yat): Which; सुख (sukha): Happiness or pleasure; विन्दति (vindati): Attains or experiences; सः (saḥ): That; एव (eva): Indeed; ब्रह्मयोगयुक्तात्मा (brahmayogayuktātmā): is 'brahmayogayuktātmā'; चेत् (cet): If; तदेव (tadeva): That alone; अक्षयं (akṣayaṁ): Imperishable / increasing; विन्दति (vindati): Attains or experiences; ब्रह्मविषयः (brahmaviṣayaḥ): On the topics concerning Brahman; योगः (yogaḥ): Yoga or discipline; ब्रह्मयोगः (brahmayogaḥ): is 'brahmayogaḥ'; ध्यानादियुक्तस्यैव (dhyānādiyuktasyaiva): Of the one engaged in meditation etc. alone; आत्मसुखं (ātmasukhaṁ): Self-happiness; अक्षयम् (akṣayam): everlasting / not diminishing; अन्यथा (anyathā): Otherwise; न (na): Not; इति (iti): Thus or in this way; अर्थः (arthaḥ): is the meaning;]

The happiness experienced by one who is without desire, that same happiness in everlasting proportion without diminishing, is experienced by one who engages in 'Brahma Yōga'. Practice of Yōga on the topics concerning Brahman is 'Brahma Yōga'. By engaging in meditation (Dhyāna) alone, the happiness of self becomes everlasting and undiminishing. Otherwise not, is the meaning.