Brahma Jnana is the knowledge of Brahman, the Supreme Reality – one without a second, in the Hindu philosophical system (in common parlance God). Brahma Jnanam is gained from the three fundamental texts (prasthana trayi) – Brahmasutra, Upanishads and Bhagavad Gita.
The mahavakyas (great aphoristic statements) in Upanishads briefly express the concept of Brahman, such as Brahman is reality, knowledge and infinite. The relationship between the supreme Brahman and the individual self is pointed out as “Thou art That” – (Tat Tvam Asi).
Brahman is the both the efficient and the material cause of the universe. It is omniscient, omnipotent and omnipresent. All the creations in the universe are produced from it and get merged into it. Thus the entire universe, along with the sentient and non-sentient beings in it, is a manifestation of the Brahman. Though it is one, it is beheld as manifold. The concept of the identity of the individual self with the supreme Brahman is the ultimate and it leads to the identity of all the individual selves.
Mundaka Upanishad classifies knowledge as aparavidya (knowledge of the texts) and paravidya (experience of perfect identity with the Supreme Self, the former consisting of Vedas and all other related texts and the latter denoting the knowledge about Brahman.
According to monism, the knowledge about the identity of Brahman, the individual selves and matter and the realization that the world and the beings are only manifestation of the supreme reality, leads to the realization of Brahman.
“To know Brahman is to become Brahman.” Since Brahman is the highest reality and is essentially of the nature of supreme bliss, the knower of Brahman also attains bliss. In order to gain such knowledge there are four prerequisites, such as discrimination between the eternal and perishable matter, the detachment from sensual pleasures in this and the next world, the six expedients such as tranquility, self control etc., and cessation of worldly acts and desire for liberation from mundane existence.
There are certain practices leading to knowledge about Brahman, such as Sravana (listening) to great statements such as “Thou art That” from spiritual preceptors, and assimilating the ideas contained in them, manana (reflection) in order to remove doubts in what has been heard, and nididhyasana (contemplation) leading to the actual realization of Brahman.
A school of Vedantins holds the view of blending the path of knowledge and the path of action for attaining realization of Brahman. The school of Advaita refutes it since the path of action and the path of renunciation of action cannot co-exist. The knowledge of Brahman is glorified as the summon bonum leading to the cessation of mundane existence.