This is one of the minor Upaniṣads assigned to the Kṛṣṇa Yajurveda group. It is a fairly long work with 466 verses in the anuṣṭubh metre, divided into six chapters. The first chapter is a direct presentation of the teaching by the Upaniṣad. Chapters two, three and four are in the form of a dialogue between Skanda (god Subrahmaṇya) and his father Śiva. The last two are a conversation—in the question-answer form—between the disciple Nidāgha and his teacher Ṛbhu.
The following is a brief synopsis of the contents:
Description of Tejobindu (Brahman as the source of spiritual light); some sādhanas that lead to it, such as control over food, conquering anger and attachment, self-control and absence of egotism; yoga of fifteen steps comprising yama (control of senses), niyama (continuous meditation on the Self as consciousness), tyāga (renouncing the world-appearance by seeing Brahman in it), mauna (observing silence) and so on; practice of yoga and overcoming the various obstacles to it; attaining Brahman through samādhi.
This chapter describes that everything that exists is ‘akhaṇḍaikarasa’ or ‘non-dual and partless essence’ (i.e., Brahman).
Ātman is the same as Brahman which is sat-cit-ānanda or existence-consciousness-bliss. This experience can be got by practising the mantra, aham brahmāsmi, ‘I am Brahman’. This is the gist of this chapter.
Jīvanmukti (liberation while living) and videhamukti (liberation from future births) are the topics described in a highly poetical language.
This chapter describes the true nature of the ātman as identified with Paramātman. The world that is grasped through the senses has no permanent and independent existence. Bondage of the individual (jīvātman) is due to the mind which is constantly desiring things.
All the ideas given earlier are more or less repeated here.
Rules are laid down here as to whom this teaching can be given and to whom it should not be imparted.
Atheists, ungrateful ones and persons of bad character are unfit to receive it.
Only those of a pure mind and endowed with devotion to the guru are fit to be taught.
The final declaration is that even a study of this Upaniṣad is enough to give liberation!