Another quote from Bronkhorst book on Brahmins

“Brahmins, in their self-understanding, owed their special status to the fact that they knew and preserved the Veda, which includes numerous mantras that are supposed to be effective if correctly pronounced in the right circumstances. Their particular concern with the correct pronunciation of those mantras is responsible for their interest in phonetics, and for the composition of treatises dealing with this topic, either in general or focused on specific Vedic texts. The effectiveness of those mantras, furthermore, showed that these mantras, and the language of these mantras, had a close affinity with reality. Sanskrit and reality were, in their opinion, closely connected, and this is a theme that comes up again and again in Brahmanical thought.
This fundamental conviction found expression in a single encompassing vision, in which both the Sanskrit language and the Veda had their place. In this vision, Sanskrit was eternal, i.e., without beginning in time; other lan- guages were at best corruptions of the only language that really existed, viz. Sanskrit. The Veda, too, was without beginning in time, and therefore without author. It needed no author, because the Veda was the pure expression of the Sanskrit language.Studying Sanskrit and studying the Veda were therefore two sides of the same coin. This issue will be taken up in the present section.” 
And more from Bronkhorst “An innovation introduced by the new Brahmanism is the belief that the Sanskrit language—i.e., its words and sounds—are eternal, and therefore without beginning and end. Patañjali the grammarian did so, but he was not the first. Already Kātyāyana held that belief, as is clear from vārttikas such as P. 1.1.56 vt. 12: anupapannaṃ sthānyādeśatvaṃ nityatvāt. There is, on the other hand, no indication that Pāṇini had accepted it. Nor had Yāska, who uses the word nitya a few times in his Nirukta, but never in the sense ‘eternal’.216 Assuming, for simplicity’s sake, that all Brahmins adopted this new conviction of the eternality of words more or less simultaneously, and considering that Yāska is almost certainly more recent than Pāṇini,this would have happened at some time between Yāska and Kātyāyana.”