Brahma Agni is the absolute or universal self or Brahman (supreme being or supreme truth) depicted as the fire of a yajna. Brahma Agni symbolism is used in Karma Sannyasa Yoga (Bhagavad Gita Chapter 3). Explaining Karma Yoga, Krishna says that the actions, other than those for Yajna, create bondage in this world (yajnarthatkarmanonyatra lokoyam karma bandhanah – Bhagavad Gita 3.9).
Yajna means the act of offering oblation or performing tyaga (austerities) for a great cause; offering oblation in fire is the way of Vedic yajna. Self-serving actions cause bondage to the soul. Attachment of any kind brings bondage, while selfless actions for lokasamgraha (universal welfare) or actions without attachment are like the offering of oblations in fire of jnana (discerning knowledge). Sri Krishna calls such actions that are free from the will of desire as jnanagni dagdha (those burnt up in the fire of knowledge) (Bhagavad Gita 4.19).
It is sakama karma (deeds undertaken with some end in view) which bind the soul to the world through the cycle of birth and death. One who has abandoned all desires and wills (kamasankalpavarjitah, Gita 4.19) and attachment (gatasanga, gita 4.23) is a mukta (liberated soul). All his actions become offerings in the yajna of life. His consciousness is established in jnana and all his actions appear to him as oblations in Brahma Yajna. He sees that the tools for offering (arpana) oblations are Brahman, the oblation offered is Brahman, and the performer of yajna is Brahman himself. In other words, in his perception, Brahman is the instrument of offering oblations as well as the material of oblation.
Brahman is the fire in which oblation is offered. In this yajna, Brahman offers the oblation of Brahman into the Brahma Agni (Brahman as fire) with the help of Brahman.
Brahman is the totality in which the boundaries between subject, object and instrument collapse and disappear.
Sri Krishna says that he who sees his actions or deeds like this, attains Brahman (Brahmarpanam, Brahma Havirbrahmagnau Brahmanahutam…, Bhagavad Gita 4.24). Some yogi perform Devayajna while others offer yajna itself in the Brahmagni (Bhagavad Gita 4.25)