Brahma Nirvana is a state of being after the exhaustion of the fruits of past deeds (prarabdha karma). Nirvana means liberation from the cycle of birth and death, and from all bondages of the human body and mind. The material cause of the gross and subtle bodies is nescience (avidya), which will be annihilated only by knowledge of Brahman-knowledge which is opposed to it. Hence Brahman-knowledge (brahma-jnana) is absolutely necessary to get nirvana.
Every jiva (soul) gets a gross body according to his
prarabhda karma which gets transformed into jati (birth), ayus (longevity) and
experiences of happiness, misery, etc. (bhaga). Even if one exhausts all his
prarabdha karma by enjoying its fruits, one cannot expect liberation, as the
person will continue to be born again owing to the presence of the sachita
karma (accumulated karma) that slowly becomes prarabdha karma over time. Also,
a person cannot remain idle, as the person is under the influence of ignorance
or prakriti which goads him into various actions. These actions increase the
stock of accumulated karma and they in turn become prarabdha karma after
sometime, which will yield the person another body.
The knowledge of Brahman, obtained through the paths of
yoga, mentioned in Upanishads and the Bhagavad Gita (3.33, 2.72), will at once
destroy all accumulated fruits of a person’s karma (actions) and also ensure
that no further actions will bind him. He will get liberated the moment
prarabdha karma is exhausted. It is enough even if he attains this state late
in life. He will continue to be Brahman forever, hence, the name Brahma Nirvana.