At the end of the age of the Samhitās the deep knowledge in these books was almost lost; however the texts themselves were carefully preserved by special methods of recitation known as aşhţa vikŗti which are in use even today. The loss of vedic knowledge is mentioned repeatedly in the later books purāņa. It is said that the Divine Being assumed the incarnation of boar and recovered the Veda books buried in the depth. This is a symbolic way of expressing a symbolic fact which we can recognize if we pay attention to the Sanskrit words. The word for boar is varāha which also has the meaning of lifting up aroha that which is sacred vara. This symbolic legend refers to the attempt at recovering the lost or buried knowledge, buried in the realms of our subconscient.
The brāhmaņa books are the result of the attempts to recover the lost knowledge. The recovery had two stages. The first stage was to record the names or details of the hymns of the Veda Samhita recited at the various steps in the outward ritual yajna and also to record the various steps of yajna. This is the content of the initial part of the brāhmaņa books. The second stage deals with the contemplations and the philosophical issues, emphasizing the subtle nature of the yajna. This stage leads to the āranyakās and Upanishads.
We will focus here on the earlier part of the brāhmaņa books. Recall that every recension of the mantra Samhita has its associated brāhmaņa book. Thus the Aitareya brāhmaņa is associated with Rigveda Samhita which has only one recension. The Vājasaneyi mādhyandina Samhita of Shukla Yajurveda has Shatapatha brāhmaņa. This brāhmaņa book contains in itself both the āraņyaka and Upanishad portions, i.e., of its 14 books kāndās, the last book, 14th, is the āranyaka. Of this book, chapters 4 through 9 constitute the famous Bŗhadāraņyaka Upanishad. This brāhmaņa gives some details of the rituals in which the hymns of the corresponding mantra Samhita, i.e., Vājasaneyi Samhita are used. It is here we find some detail of the rituals. For example the kāndās 6 through 9 deal with the construction of the bird-shaped fire-altar in the so-called agnichayana rite. These kāndās give a ritualistic explanation of the mantrās in the adhyāyās or chapters eleven through eighteen of the vājasaneyi samhita. It is important to understand that when one reads the original of these chapters 11 through 18 of the mantra–samhita book, one barely sees any mention of the fire-altar. As a matter of fact, the chapters 16 and 18 constitute the famous litany to the deity rudra or shatarudrīya.
The tenth pravargya of the shatapatha brāhmaņa is titled agnirahasya or the secret of Agni. This chapter gives the legends and the contemplations regarding the different ritual acts associated with the mystic fire Agni. Recall that these rituals are mentioned in the earlier pravargyās six through nine. This chapter views the fire-ritual as a model of the cosmos and its dynamic activities. It sets up a correspondence between the fire-altar and three planes or worlds namely the world of the physical matter bhūh, the world of the life-energies bhuvah and the world of the mental energies suvah. The correspondence is very detailed. The fire-altar is constructed of five materials namely stones, the filling earth and three types of bricks. This 10th chapter gives the correspondences for these items to those on the three cosmic realms mentioned above.
While placing a particular type of brick during the construction of the fire-altar, the chapter 16 of the mantra-samhita, the hymn to rudra, is recited. Before the commencement of this hymn, it is stated that by this recitation the bricks become dhenavah, cows. Outwardly such a statement does not make sense. However as mentioned in the mantra samhita section dhenavah is a standard symbol for spiritual knowledge. Hence the above statement interpreted in the context of a symbolic yajna occurring in the subtle body of the performer makes sense. In this inner yajna, a symbolic fire-altar is constructed and the entire altar glows with knowledge.
Thus even though the brāhmaņa books focus on the external ritual, still there are passages, here and there, to demonstrate that the deeper meaning of yajna in the inner yajna. This deeper symbolism of yajna is given in other brāhmaņa books also. For instance aitareya brāhmaņa (2.6.3) of the rig veda states, “yajamāna himself is the fire-altar”. The detailed quotation is given in later chapters.