This is a small Upaniṣad of 38 verses belonging to the Kṛṣṇa Yajurveda and classified among the ‘Yoga Upaniṣads’ since the subject matter relates to yoga.
The Upaniṣad starts with the exhortation to study the scriptures like the Vedas and their accessories, practise the disciplines taught there, realize the highest Brahman and then, give up these scriptures since the purpose of life will have been accomplished.
This is followed by a simile of the chariot in which Om is the chariot and Viṣṇu (= buddhi or intellect) is the charioteer. The aspirant devoted to Rudra (his own Self) and desirous of attaining Brahmaloka or the abode of Brahman, travels in that chariot as far as it goes and then abandons it. The idea is that the aspirant while repeating Om thinks of ‘Rudra’ or his own Self as identified with Brahman, through his intellect. When this identity is felt, he abandons the repetition of Om but proceeds to make his meditation deeper, ultimately resulting in direct experience of that oneness.
Then comes the description of ‘Ṣaḍaṅga-yoga’ or yoga comprising six steps. They are: pratyāhāra, dhyāna, prāṇāyāma, dhāraṇā, tarka and samādhi. Pratyāhāra (lit., withdrawal of the mind from the senses) is defined here as thinking of the mind and the sense-objects as ‘rays emanating from the ātman’ thus neutralizing their effects. Dhyāna is meditation on the oneness of ātman with Brahman. Prāṇāyāma is regulation of breath, and through that, regulation of the vital energies or prāṇas. Dhāraṇā or fixing the mind on the objects of meditation, is the earlier stage of dhyāna. Tarka is logic, not opposed to the teachings of the Vedas. Samādhi is the direct experience of the oneness of the ātman with Brahman.
The Upaniṣad gives some details of the process of prāṇāyāma, positions and fields of operation of the five prāṇas, certain obstacles to yoga like fear, anger and laziness which must be overcome and a few other details connected with yogic practices. It concludes with the statements that if a yogi has mastered the techniques of raising his prāṇa through the various plexuses up to the centre of the head, his prāṇa will depart, at the time of death, through the brahmarandhra (aperture in the crown of the head) whatever be the manner of his death, and so, he is never reborn.