The characteristics of agniṣṭoma yajña (agnishtoma yajna) encapsulate the essence of the entire somayajña (somayajna). Those yajña the details which have been directly laid down by the śruti (shruti; another name of Veda) are known as prakṛti (prakriti) or ‘essence’. Aitareya Brāhmaṇa (Aitareya Brahmana) carries an anecdote about how agniṣṭoma yajña came into being. It is said that in the days of old, the gods were once all set to attack the demons in order to conquer them. However, Agni, the Fire-god, refused to join the expedition. When the other gods pleaded, Agni said, “I shall not come along unless you sing praise of mine.” The helpless gods finally had to sing praise of Agni. Agni, now pleased, divided the three Vedic poetic meters, namely gāyatrī (gayatri), triṣṭupa (trishtupa) and jagatī (jagati), into three battalions and converted the items of yajña into soldiers and marched off to war. The gods emerged winner in this war.
Those eulogies uttered by the gods gave birth to agniṣṭoma yajña, which heralded the gods’ victory in the war. Since the gods had worshipped Agni with verses or stoma, the yajña came to be known as agniṣṭoma. The word agniṣṭoma has its root in the word agnistoma. Agniṣṭoma has unity of spirit with gāyatrīmantra, as gāyatrī has twenty-four sylables and agniṣṭoma incorporates twenty-four verses (or weapons, as the gods used the verses as weapons). Agniṣṭoma has the same effect as Gāyatrī, which rewards the performer of the yajña with the (spiritual) elixir of life. Agniṣṭoma has also been compared to a full year. A full year has twenty-four half-months and the agniṣṭoma, too, has twenty-four verses (weapons). The dignity enjoyed by agniṣṭoma is so high that it is said that all offerings made at all forms of yajña finally make their way into agniṣṭoma, just as all rivers find their way into the ocean. Vedas have ruled that the person desiring to reach the heavens should perform agniṣṭoma yajña, observing all the prescribed norms.