the number seven plays plays an exceedingly important part in vedic system, as in most very ancient school of thoughts. we find it recurring constantly, - the seven delights, " सप्त रत्नानी "; the seven flames, tongues or rays of agni, "सप्त ज्वालः "; seven forms of the thought principle, "सप्त धितायः " ; seven rays or cows " सप्त गवः "; seven mothers or fostering cows "सप्त मातृ" , "सप्त धेनवः ". all these set of seven depends upon vedic classification of fundamental principles, the tattvas of existence. these seven principles are : 1. pure existence - सत ; 2. pure consciousness - चित ; 3. pure bliss - आनंद ; 4. knowledge of truth - विज्ञान ; 5. mind; 6. life; 7. matter.
in the veda then we find the number of principles variously stated. the one was recognised as basis and continent; in this were two principles divine and human, mortal and immortal. the dual number is also otherwise applied in two principles, heaven and earth, mind and body, soul and nature, who are regarded as the father and mother of all beings.
the triple principle was doubly recognized, first in the threefold mundane principle, mind,life, body upon built the triple world of veda and puranas. but full number ordinarily recgnised is seven. this figure was arrived at by adding the three divine principles to the three mundane.
also the seven rivers are conscious currents corresponding to the sevenfold substance of ocean of being which appears to us formulated in the seven worlds enumerated by puranas. it is their full flow in human consciousness which constitutes the entire activity of being, his full treasure of substance, his full play of energy. in vedic image, his cows drink of the water of the seven rivers.