समं कायशिरोग्रीवं धारयन्नचलं स्थिरः ।
संप्रेक्ष्य नासिकाग्रं स्वं दिशश्चानवलोकयन् ॥ १३ ॥ (6.13)
प्रशान्तात्मा विगतभीर्ब्रह्मचारिव्रते स्थितः ।
मनः संयम्य मच्चित्तो युक्त आसीत मत्परः ॥ १४ ॥ (6.14)
(13) Holding the body, head and neck erect and still, being steady, looking at the tip of his own nose–and not looking in various directions–,
(14) –with a placid mind, free from fear, firm in the vow of a celibate, and with the mind fixed on Me after controlling it, and having Me as the supreme Goal, he should remain seated, absorbed in संप्रज्ञात-समाधि.
काय is the middle part of the body. (The Tamil word காயம் came from Sanskrit काय – as in காயமே இது பொய்யடா!).
That and the head and the neck constitute काय-शिरो-ग्रीव. धारयन्, holding; समं, erect, unbent; and अचलम्, still.
तत्प्रतिषेधार्थमेकतत्त्वाभ्यासः॥३२॥ (Patanjali Yoga Sutra 1.32-32)
the body from the lowest end of the spinal column to the crown of the head–by eliminating through the practice of concentration on one object the tremors in the body that accompany distractions of the mind; being स्तिरः, steady in effort; and further, संप्रेक्ष्य, looking; only स्वं नासिकाग्रं, at the tip of his own nose–i.e. remaining with the eyes not fully closed, and without any inclination towards objects–, for avoiding लय (mental inactivity) and विक्षेप (distraction); च, and; अनवलोकयन्, not looking; दिशः, in various directions now and then; for that is an obstacles to Yoga;–becoming thus, आसीत, he should remain seated. This is how it is to be connected with the later portion (of the body).
Let me quote Shankara Bhaashyam here:
प्रशान्तात्मा प्रकर्षेण शान्तः आत्मा अन्तःकरणं यस्य सोऽयं प्रशान्तात्मा, विगतभीः विगतभयः, ब्रह्मचारिव्रते स्थितः ब्रह्मचारिणो व्रतं ब्रह्मचर्यं गुरुशुश्रूषाभिक्षान्नभुक्त्यादि तस्मिन् स्थितः, तदनुष्ठाता भवेदित्यर्थः । किञ्च, मनः संयम्य मनसः वृत्तीः उपसंहृत्य इत्येतत्, मच्चित्तः मयि परमेश्वरे चित्तं यस्य सोऽयं मच्चित्तः, युक्तः समाहितः सन् आसीत उपविशेत् । मत्परः अहं परो यस्य सोऽयं मत्परो भवति । कश्चित् रागी स्त्रीचित्तः, न तु स्त्रियमेव परत्वेन गृह्णाति ; किं तर्हि ? राजानं महादेवं वा । अयं तु मच्चित्तो मत्परश्च ॥
Besides, प्रशान्तात्मा, with a placid mind–one having his mind absolutely tranquil, free from such defects as attachment etc. as a result of the cessation of their primal cause–; विगतभी:, free from fear–one whose fear, doubt and right and wrong, has been dispelled as a consequence of his having renounced all actions through firmness of his scriptural convictions; remaining स्थितः, firm; ब्रह्मचारि-व्रते, in the vow of a celibate–in celibacy, service to guru, living on alms, etc; and संयम्य, after controlling; मनः, the mind–i.e. making it free of thinking of objects–; then मच्चित्त:, having the mind fixed on Me, the supreme Lord, the inmost Consciousness, conditioned or unconditioned; having a flow of thoughts with regard to me–.
How can this be so, since, one has to think about his sons etc. which are dear? Hence Bhagavan Krishna says:
मत्परः, having Me as the supreme Goal, i.e. becoming one to whom I Myself am the Supreme, the cherished human Goal, because of being supreme Bliss by nature as the Sruti says:
तदेतत्प्रेयः पुत्रात्प्रेयो वित्तात्प्रेयोऽन्यस्मात्सर्वस्मादन्तरतरं यदयमात्मा । (बृहदारण्यकोपनिषद्भाष्यम् 1.4.8)
This Self is dearer than a son, dearer than wealth, dearer than everything else, and is the innermost.
Thus having a single thought in the form of the Lord by totally obliterating all other thoughts of objects, असित, he should remain seated; युक्तः, absorbed in संप्रज्ञात-समाधि; but he should not emerge from it at will. This is the meaning.
There may be some passionate person with his mind on his wife, but he does not accept the wife herself as the highest and the adorable. What then? He accepts a boss or a king as a deity.
But this one yogi with his mind fixed on Me and having Me as the Supreme, accepts Me alone as the one to be adored by all. This is Sankara’s commentary.