(From 'Religious Riddles' in Part I of the book 'Riddles in Hinduism' by Babasaheb Dr. B. R. Ambedkar)
There is hardly any Hindu who does not regard the Vedas as the most sacred Book of his religion. And yet ask any Hindu what is the origin of the Vedas and it would be difficult to find one who can give a clear and a definite answer to the simple question. Of course, if the question was addressed to a Vedic Brahmin he would say that the Vedas are Sanatan. But this is no answer to the question. For first of all what does the word Sanatan mean?
The best explanation of the word Sanatan is to be found in the commentary by Kulluka Bhatt on Chapter I Shlokas 22-23 of the Manu Smriti. This is how Kulluka Bhatt defines the word Sanatan1.
"The word Sanatana he says, means 'eternally pre-existing'. The doctrine of the superhuman origin of the Vedas is maintained by Manu. The same Vedas which (existed) in the previous mundane era (Kalpa) were preserved in the memory of the omniscient Brahma, who was one with the supreme spirits. It was those same Vedas that, in the beginning of the present Kalpa, he drew forth from Agni, Vayu and Surya; and this dogma, which is founded upon the Veda, is not to be questioned, for the Veda says, 'the Rig-Veda comes from Agni, the Yajur-Veda from Vayu, and the Sama-Veda from Surya." To understand the explanation by Kulluka Bhatt it is necessary to explain what Kalpa means.