The Circular Nature of the Microcosmic Yajna

 With them, again, those men [neuronal beings] who take the law for their light perform daily sacrifices [dichotomizations], and through them give nourishment [oxygenated blood] to the gods [superior / controlling neural entities]. And thus sacrifices, the Vedas [respiratory bronchioles], the four castes [four groups of neural entities], with the Brahmans at their head, all the residences of the gods [the higher bronchi], all the tribes of animals [the different bronchial and bronchiolar conduits], the whole world [respiratory world], all are supported by the rains [the pulmonary flow] by which food [oxygenated blood] is produced.

The respiratory mechanism has a circular nature built into it. This is also hinted at in the Gita. The neural entities are nourished through respiration. The flow of oxygen molecules is verily ambrosia for the inhabitants of the microcosm because it sustains the bronchial apparatus. Again, it is this apparatus and the activity of the neurons on it that keeps respiration going. So one influences the other in a circular way. The external yajna is an emulation of this microcosmic reality. Here the vedi, sacrificial altar, represents the bronchial tree. But it must be remembered that a mere mimicking of respiratory physiology cannot be the objective of this exercise. Indeed it would be absurd, if not outright crazy, to claim that the external universe, like the internal one, is maintained through such an activity. The real objective is progressive spiritual education; to educate the participant in this exercise regarding the supreme purusa – the ultimate supporter and the supreme cause of this life-supporting apparatus. The purpose is to focus the vision of the initiate inwards; to make him antarmukhi so that he realizes that what is being emulated outside forms the most vital process of his own body and that the supporter of such a process is the supreme controlling entity (parama deva) Lord Narayana himself, to whom exclusively one's devotion ought to be directed.  The succeeding Visnu Purana lines declare this supreme truth:

But the rain is evolved by the sun; the sun is sustained by Dhruva; and Dhruva is supported by the celestial porpoise-shaped sphere, which is one with Náráyańa. Náráyańa, the primeval existent, and eternally enduring, seated in the heart of the stellar sphere, is the supporter of all beings.

Note: the "celestial porpoise-shaped sphere" in the quote above is the pulmonary arterial realm which is held by the developers of the microcosmic model as the support of the entire universe. But even this great supporting entity is ultimately supported by the Lord. This is the point that the author wants to make in the passage above.