Verse 1.10

अथोत्तरेण तपसा ब्रह्मचर्येण श्रद्धया विद्ययात्मानमन्विष्यादित्यमभिजयन्ते । एतद्वै प्राणानामायतनमेतदमृतमभयमेतत् । परायणमेतस्मान्न पुनरावर्तन्त इत्येष निरोधस्तदेष श्लोकः ॥ १० ॥

athottareṇa tapasā brahmacaryeṇa śraddhayā vidyayātmānamanviṣyādityamabhijayante । etadvai prāṇānāmāyatanametadamṛtamabhayametat | parāyaṇametasmānna punarāvartanta ityeṣa nirodhastadeṣa ślokaḥ || 10 ||

10. Now, by the northern route, by tapas, Brahmacharya, faith and knowledge seeking after the atman, they gain the sun. This is the stay of all lives, this is immortal, this is fearless, the highest goal; they do not return from thence. This is the obstacle. About that, is this (following) verse.

Shankara’s Commentary:

Com.—By the northern route, they reach the sun, a part of the lord of creation, the prana, the eater. By what? by tapas, i.e., by control over the senses, more particularly by Brahmacharya, by faith and by knowledge regarding the self of the lord of creation, i.e., worship of Prajapati; seeking after the self, i.e., the prana, the sun, the stay of the universe, i.e., realising the sun in the form ‘I am he,’ they gain, i.e., reach the sun. This is certainly the common abode of all lives, their support; this is immortal, i.e., indestructible and, therefore, fearless, not full of fear of increase or diminution like the moon. This is the highest goal of those who resort to mere worship and of those who combine karma and worship. They da not return from hence, as followers of mere karma do: Hence, this is, the obstacle of the ignorant; for, the ignorant obstructed by the sun do not attain the year, i.e., the sun, i.e., the prana. He, the year, in the nature of time, is an obstacle to the ignorant About that, is the following verse.