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Bg 6.15

yuñjann evaṁ sadātmānaṁ
yogī niyata-mānasaḥ
śāntiṁ nirvāṇa-paramāṁ
mat-saṁsthām adhigacchati
Synonyms: 
yuñjan — practicing; evam — as mentioned above; sadā — constantly; ātmānam — body, mind and soul; yogī — the mystic transcendentalist; niyata-mānasaḥ — with a regulated mind; śāntim — peace; nirvāṇa-paramām — cessation of material existence; mat-saṁsthām — the spiritual sky (the kingdom of God); adhigacchati — does attain.
Translation: 
Thus practicing constant control of the body, mind and activities, the mystic transcendentalist, his mind regulated, attains to the kingdom of God [or the abode of Kṛṣṇa] by cessation of material existence.
Purport: 

The ultimate goal in practicing yoga is now clearly explained. Yoga practice is not meant for attaining any kind of material facility; it is to enable the cessation of all material existence. One who seeks an improvement in health or aspires after material perfection is no yogī according to Bhagavad-gītā. Nor does cessation of material existence entail one’s entering into “the void,” which is only a myth. There is no void anywhere within the creation of the Lord. Rather, the cessation of material existence enables one to enter into the spiritual sky, the abode of the Lord. The abode of the Lord is also clearly described in the Bhagavad-gītā as that place where there is no need of sun, moon or electricity. All the planets in the spiritual kingdom are self-illuminated like the sun in the material sky. The kingdom of God is everywhere, but the spiritual sky and the planets thereof are called paraṁ dhāma, or superior abodes.

A consummate yogī, who is perfect in understanding Lord Kṛṣṇa, as is clearly stated herein by the Lord Himself (mat-cittaḥ, mat-paraḥ, mat-sthānam), can attain real peace and can ultimately reach His supreme abode, Kṛṣṇaloka, known as Goloka Vṛndāvana. In the Brahma-saṁhitā (5.37) it is clearly stated, goloka eva nivasaty akhilātma-bhūtaḥ: the Lord, although residing always in His abode called Goloka, is the all-pervading Brahman and the localized Paramātmā as well by dint of His superior spiritual energies. No one can reach the spiritual sky (Vaikuṇṭha) or enter into the Lord’s eternal abode (Goloka Vṛndāvana) without the proper understanding of Kṛṣṇa and His plenary expansion Viṣṇu. Therefore a person working in Kṛṣṇa consciousness is the perfect yogī, because his mind is always absorbed in Kṛṣṇa’s activities (sa vai manaḥ kṛṣṇa-padāravindayoḥ). In the Vedas also (Śvetāśvatara Upaniṣad 3.8) we learn, tam eva viditvāti mṛtyum eti: “One can overcome the path of birth and death only by understanding the Supreme Personality of Godhead, Kṛṣṇa.” In other words, perfection of the yoga system is the attainment of freedom from material existence and not some magical jugglery or gymnastic feats to befool innocent people.