[5] The Brihadaranyaka Upanishad is a treatise on Ātman (Self), includes passages on metaphysics, ethics, and a yearning for knowledge that influenced various Indian religions, ancient and medieval scholars, and attracted secondary works such as those by Adi Shankara and Madhvacharya.

[8] Patrick Olivelle states, "in spite of claims made by some, in reality, any dating of these documents (early Upanishads) that attempts a precision closer than a few centuries is as stable as a house of cards".

Then, Prajapati created the universe from this nothingness as a sacrifice to himself, imbuing it with Prana (life force) to preserve it in the form of cosmic inert matter and individual psychic energy.

[11][14] The Brihadaranyaka Upanishad asserts that the world is more than just matter and energy; it is also constituted by Atman or Brahman (Self, Consciousness, Invisible Principles, and Reality) as well as Knowledge.

[18][19] This theory appears in various early and middle Upanishads, and parallels Immanuel Kant's doctrine of "the affinity of phenomena" built on "the synthetic unity of apperception".

[18][21] The third chapter is a metaphysical dialogue between ten ancient sages, on the nature of Reality (Brahman), Atman (individual self), and Mukti (liberation).

[22][23] Paul Deussen calls the presentation of ancient scholar Yajnavalkya in this chapter "not dissimilar to that of Socrates in the dialogues of Plato".

[24] Among other things, the chapter presents the theory of perceived empirical knowledge using the concepts of graha (sensory action) and atigraha (sense).

It lists 8 combinations of graha and atigraha: breath and smell, speech and name (ideas), tongue and taste, eye and form, ear and sound, skin and touch, mind and desire, arms and work respectively.

This marks the beginning of the journey toward profound knowledge and understanding the Self of all things, where freedom from frustration and sorrow is found.

In these brahmanas, Gargi Vachaknavi and Yajñavalka engage in philosophical inquiries and debates, exploring the ultimate truth and the imperishable nature of reality.

The discussions explore deep philosophical ideas, highlighting the importance of seeking spiritual wisdom and the quest to understand the timeless, unchanging reality that transcends the material world.

[27] The seventh brahmana explores the interconnectedness of the Self with all of existence, emphasizing its role as the inner controller, often without the knowledge of beings.

[29][30] The last hymns of chapter 3 in Brihadaranyaka Upanishad also attest to the prevalent practice of the renouncing ascetic life by the time Brihadaranyaka Upanishad was composed in Vedic age of India, and it is these ascetic circles that are credited for major movements such as Yoga as well as the śramaṇa traditions later to be called Buddhism, Jainism and heterodox Hinduism.

In the first brahmanam of the fourth chapter, the Upanishad states that the Self manifests in human life in six forms: Prajna (consciousness), Priyam (love and the will to live), Satyam (reverence for truth, reality), Ananta (endlessness, curiosity for the eternal), Ananda (bliss, contentness), and Sthiti (the state of enduring steadfastness, calm perseverance).

[35] The hymn 4.2.4 of Brihadaranyaka Upanishad is one of many instances in the ancient Sanskrit text where the characters involved in philosophical debate greet each other with Namaste (नमस्ते), a practice in the culture of India.

[36] The third brahmanam of the fourth chapter discusses the premises of moksha (liberation, freedom, emancipation, self-realization), and provides some of the most studied hymns of Brihadaranyaka.

Paul Deussen calls it, "unique in its richness and warmth of presentation", with profoundness that retains its full worth in modern times.

The fourth brahmanam continues to build the thematic description of Atman-Brahman (Self) and the state of self-realization as achieved.

In hymn 4.4.22, the Upanishad states:[39] He is that great unborn Self, who consists of Knowledge, is surrounded by the Prânas (life-force), the ether within the heart.

[35][40] The fifth and sixth chapters of Brihadaranyaka Upanishad are known as Khila Khanda, which literally means "supplementary section, or appendix".

This section, suggests Paul Deussen, was likely written later to clarify and add ideas considered important in that later age.

[43] In the fourth brahmanam of sixth chapter, sexual rituals between a husband and wife are described to conceive and celebrate the birth of a child.

A key figure in this process is the deity Prajapati, who creates the world through liturgical recitation, priestly sacrifice, dividing up his own body, copulation, giving birth to various devas and demons.

This brahman in the space of the heart is said to be "the controller of all, the lord of all, the ruler of all," and is not affected or changed by karma (action).

This brahman in the heart, also called Prajapati, is also described in the Bṛhadāraṇyaka as follows:This person here is made of mind and consists of light.

— Brihadaranyaka Upanishad 4.4.5[79] Ancient and medieval Indian scholars have referred to the Bṛhadāraṇyaka Upaniṣad as a foundation for discussing psychological theories, the nature of psyche, and the interactions between body, mind, and Self.

In these secondary texts, the same passages have been interpreted in differently by various sub-schools of Vedanta, including Advaita (monism), Dvaita, and Vishistadvaita.

This perspective emphasizes the infinite and glorious nature of the Divine, suggesting that the negation is more about the limitation of our understanding than about Brahman itself.

[87][88] Poet T. S. Eliot makes use of the story "The Voice of the Thunder" and for the source of "datta, dayadhvam, and damyata" found in the Brihadaranyaka Upanishad.