They are the breath of the Eternal.

As smoke and sparks arise from a lighted Fire kindled With damp fuel, even so, Maitreyi. 
have breathed forth from the Eternal all 
knowledge and all tutsdom — what we know 
as the Rig Veda, the Yajur Veda, and the 
rest. They are the breath of the Eternal. 

— BRIHADARANYAKA