B.G 8.12 and 13
सर्वद्वाराणि संयम्य मनो हृदि निरुध्य च। मूर्ध्न्याधायाऽत्मनः प्राणमास्थितो योगधारणाम् ॥१२॥
Having restrained all the gates, fixing the mind in the lord Nārāyaṇa, placing the breath in the head, one remains established in the practice of yoga.
ओमित्येकाक्षरं ब्रह्म व्याहरन् मामनुस्मरन्। यः प्रयाति त्यजन् देहं स याति परमां गतिम् ॥१३॥
Whoever, uttering the one-syllabled Om, which is Brahman, and remembering Me, departs leaving the body, attains the supreme destination.
Gīta Bhāshya 8.12 and 13
It is not possible to have the mind in the heart and to place the breath in the head. Wherever lies the vital breath, the supreme Prāṇa, there lies the mind, and the living being. So the word 'hṛdi' in the current context means lord Nārāyaṇa. A testimonial is given to substantiate the same - "Because you take away the world, you are indeed called 'hṛdi'". 'yogadhāraṇām' means being engrossed in Yoga alone.
ब्रह्मनाडीं विना यद्यन्यत्र गच्छति तर्हि विना मोक्षं स्थानान्तरं प्राप्नोति इति सर्वद्वाराणि संयम्य।
If one departs through any other passage without the Brahman-nāḍī, then, without attaining liberation, one reaches another state of existence. Therefore one should restrain all other openings.
"निर्गच्छन् चक्षुषा सूर्यं दिशः श्रोत्रेण चैव हि॥"
"Departing (from the body) through the eye one reaches the Sun, and through the hearing the directions."
इति वचनात् व्यासयोगे। मोक्षधर्मे च।
- it is stated thus in the Vyāsa-yoga. Same is stated in the Mokṣa-dharma (section of the Mahabharata) as well.
हृदि नारायणे।
The phrase 'In the heart' means in lord Nārāyaṇa.
"ह्रियते त्वया जगद्यस्मात् हृदित्येव प्रभाष्यसे॥"
"Because you take away the world, you are indeed called 'hṛdi'."
इति पाद्मे।
- stated thus in the Padma Purāṇa.
न हि मूर्धनि प्राणे स्थिते र्हृदि मनसः स्थितिः सम्भवति -
Indeed, when the vital breath is situated in the head, the stability of the mind in the heart is not possible:
"यत्र प्राणो मनस्तत्र तत्र जीवः परस्तथा॥"
"Wherever lies the vital breath, the supreme Prāṇa, there lies the mind, and the living being."
इति व्यासयोगे।
- stated thus in Vyāsayoga.
योगधारणाम् आस्थितः योगभरणे एव अभियुक्तः इत्यर्थः ॥१२, १३॥
The word 'yogadhāraṇā' means being engrossed in yoga alone — this is the intended meaning.
Gīta Tātparya 8.12 and 13
'ekākṣaram' - the Supreme Brahman.
एकाक्षरवाच्यत्वात् एकाक्षरं परं ब्रह्म ॥१३॥
Since the Supreme Brahman is conveyed by the single syllable (Oṁ), he is called 'ekākṣaram', i.e. single syllable.
