In plain words
Holding body, head, and neck straight and steady, unmoving, with the gaze resting as if on the tip of one's own nose and not looking around,
Word for word
Holding body, head and neck straight [and] unmoving, steady, [as if] gazing at the tip of one's own nose, and not looking about at the directions,
समं कायशिरोग्रीवं धारयन्नचलं स्थिरःसम्प्रेक्ष्य नासिकाग्रं स्वं दिशश्चानवलोकयन्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
बाह्यमासनमुक्तम् ; अधुना शरीरधारणं कथम् इत्युच्यते —
समं कायशिरोग्रीवं कायश्च शिरश्च ग्रीवा च कायशिरोग्रीवं तत् समं धारयन् अचलं च । समं धारयतः चलनं सम्भवति ; अतः विशिनष्टि — अचलमिति । स्थिरः स्थिरो भूत्वा इत्यर्थः । स्वं नासिकाग्रं सम्प्रेक्ष्य सम्यक् प्रेक्षणं दर्शनं कृत्वेव इति । इवशब्दो लुप्तो द्रष्टव्यः । न हि स्वनासिकाग्रसम्प्रेक्षणमिह विधित्सितम् । किं तर्हि ? चक्षुषो दृष्टिसंनिपातः । स च अन्तःकरणसमाधानापेक्षो विवक्षितः । स्वनासिकाग्रसम्प्रेक्षणमेव चेत् विवक्षितम् , मनः तत्रैव समाधीयेत, नात्मनि । आत्मनि हि मनसः समाधानं वक्ष्यति ‘आत्मसंस्थं मनः कृत्वा’(भ. गी. ६ । २५) इति । तस्मात् इवशब्दलोपेन अक्ष्णोः दृष्टिसंनिपात एव ‘सम्प्रेक्ष्य’ इत्युच्यते । दिशश्च अनवलोकयन् दिशां च अवलोकनमन्तराकुर्वन् इत्येतत् ॥ १३ ॥
In plain words
The outer seat has been covered. Now: how is the body itself to be held? This is what is said next —
Hold body, head, and neck level and unmoving—body, head, neck together, kept level and still. Level alone still leaves room to sway, so the verse adds ‘unmoving’ too. ‘Steady’ simply means having become steady. ‘Gazing at the tip of his own nose’ really means gazing properly, seeing, as if at it—there's an unspoken ‘as if’ folded into the phrase, because literally staring at your own nose-tip isn't actually what's meant here. What is meant? Just letting the two eyes' gaze converge and settle, which depends on the mind itself being composed. If literal nose-tip gazing were really meant, the mind would fix itself right there, on the nose, not on the Self. But Kṛṣṇa will soon teach fixing the mind in the Self itself—‘having made the mind rest in the Self’ (6.25). So, filling in that missing ‘as if,’ ‘gazing’ simply means letting the two eyes' gaze converge, nothing more. And ‘not looking at the directions’ just means not letting your eyes wander around the room.
Close to the Sanskrit
The external seat has been spoken of; now, how the holding of the body [is to be done] — thus it is said —
Holding the body, head, and neck—body and head and neck—that complex, level, and unmoving. For one who holds it merely level, movement is still possible; therefore the text further specifies ‘unmoving.’ ‘Steady’ means having become steady—that is the meaning. ‘Having gazed at the tip of his own nose’—that is, having done a proper looking, a seeing, as if—that is the sense; the word ‘as if’ is to be understood as elided. For the literal gazing at the tip of one's own nose is not, indeed, what is intended here. What then is meant? The convergence of the gaze of the two eyes; and that is intended as dependent on the composure of the mind. If the literal gazing at the tip of the nose alone were intended, the mind would become fixed right there, not in the Self. For Kṛṣṇa will teach the fixing of the mind in the Self: ‘having made the mind fixed in the Self’ (BG 6.25). Therefore, by supplying the elided word ‘as if,’ the mere convergence of the gaze of the two eyes is what is meant by ‘gazing at.’ ‘And not looking at the directions’ means not making a looking-around at the directions—that is what is meant.