The Mandukya Upanishad (Sanskrit: माण्डूक्योपनिषद्, IAST: Māṇḍūkyopaniṣad) is the shortest of all the Upanishads, and is assigned to Atharvaveda. It is listed as number 6 in the Muktikā canon of 108 Upanishads.
It is in prose, consisting of twelve short verses, and is associated with a Rig Vedic school of scholars. It discusses the syllable Aum; adds turiya to the three states of consciousness; and asserts that Aum is Brahman – which is the Whole – and that Brahman is this self (ātman).
The belief that God became the Universe is a theological doctrine that has been developed several times historically, and holds that the creator of the universe actually became the universe. Historically, for versions of this theory where God has ceased to exist or to act as a separate and conscious entity, some have used the term pandeism, which combines aspects of pantheism and deism, to refer to such a theology. A similar concept is panentheism, which has the creator become the universe only in part, but remain in some other part transcendent to it, as well. Hindu texts like the Mandukya Upanishad speak of the undivided one which became the universe.
The Mahāvākyas (sing.: mahāvākyam, महावाक्यम्; plural: mahāvākyāni, महावाक्यानि) are "The Great Sayings" of the Upanishads, with mahā meaning great and vākya, a sentence. The Mahāvākyas are traditionally considered to be four in number, though actually five are prominent in the post-Vedic literature:
Mahāvākyas are instrumental in Advaita Vedanta, as they are regarded as valid scriptural statements that reveal the self (ātmán), which appears as a separate individual existence (jīva), is, in essence, non-different (not two-ness) from Brahman, which, according to Advaita, is nirguna. In contrast, these statements are less prominent in most other Hindu traditions, which emphasize a qualified or dualistic relationship between the self and Brahman, whom they regard as saguna, often identified with Vishnu, Shiva, Shakti, etc.
Prasthanatrayi (Sanskrit: प्रस्थानत्रयी, IAST: Prasthānatrayī), literally, three sources (or axioms), refers to the three canonical texts of theology having epistemic authority, especially of the Vedanta schools. It consists of:
The Upanishads consist of ten, twelve or thirteen major texts, with a total of 108 texts (some scholars list ten as principal – the Mukhya Upanishads, while most consider twelve or thirteen as principal, most important Upanishads). The ten Upanishads are Īśā, Kena, Kaṭha, Praṣna, Muṇḍaka, Māṇḍūkya, Taittirīya, Aitareya, Chāndogya and Bṛhadāraṇyaka.