The context of the whole discussion is set by Krishna talking about a class of transcendentalists whose goal is to get liberated from old age and death (BG 7.29). Please refer here for details. It is important to note that the pure devotional yogis (bhakti yogis) on the other hand are exclusively motivated by pure love for Krishna (referred to in BG 7.28) and therefore operate at a higher level than these self-motivated transcendentalists.
At the time of death (prayāṇa-kāle), with an undeviating mind (manasācalena), and filled with devotion (bhaktyā yukto), by the strength of yoga (yoga-balena), completely (samyak) fixing the life air between the eyebrows (bhruvor madhye prāṇam āveśya), one reaches that Supreme Divine Person (paraṁ puruṣam upaiti divyam). (BG 8.10) The fixing of the life air between the eyebrows facilitates remembrance of Krishna.
The learned sages (veda-vido) talk about the indestructible place (akṣaraṁ) into which the endeavoring transcendentalists (yatayo) free from attachment (vīta-rāgāḥ) enter (viśanti). While desiring to go there, they practice celibacy (brahma-caryaṁ). Krishna will now briefly touch upon the process as well as the place. (BG 8.11)
Restraining all the gates (senses) of the body (sarva-dvārāṇi saṁyamya), fixing the mind on the heart (mano hṛdi nirudhya) and the life air on the top of the head (mūrdhny ādhāyātmanaḥ prāṇam), one stands on the platform of yoga (yoga-dhāraṇām). (BG 8.12) Then, vibrating (vyāharan) the Absolute (brahma) as the single syllable (ekākṣaraṁ), oṁ, one who quits this world by leaving the body (yaḥ prayāti tyajan dehaṁ) attains the highest destination (paramāṁ gatim). (BG 8.13) Note the perfect synthesis of the indestructible Brahman (BG 8.3), the indestructible destination (BG 8.11), and the indestructible oṁ (BG 8.13) in the word, akṣaraṁ.
What about the pure devotional yogis (bhakti yogis) that Krishna talked about in BG 7.28? For one who always (satataṁ) and regularly (nityaśaḥ) remembers Krishna (yo māṁ smarati) without any other deviation (ananya-cetāḥ), Krishna (ahaṁ) becomes very easy (su-labhaḥ) to attain because of constant engagement with Krishna (nitya-yuktasya). (BG 8.14)
What does it mean by attaining Krishna? It means returning back to Krishna’s abode where we originally belong. Upon attaining Krishna (mām upetya), the great souls (mahātmānaḥ) never take (nāpnuvanti) birth again (punar janma) in this temporary world (mām upetya), which is full of miseries (duḥkhālayam). They are considered to have attained supreme (paramāṁ) perfection (saṁsiddhiṁ). (BG 8.15) Why is this such a big deal? From the highest planet of Lord Brahmā to the lowest (ā-brahma-bhuvanāl lokāḥ) in this material world, all are places where repeated birth and death (punar āvartino) take place. But (tu), on reaching Krishna (mām upetya), one is never born again (punar janma na vidyate). (BG 8.16)
