p. 238
यतो न वेदा मनसा सहेनमनुप्रविश्यन्ति ततोऽथ मौनम् ।
In plain words
The Vedas, and the mind along with them, cannot get inside him. That is why it is called mauna — silence.
Close to the Sanskrit
Since the Vedas, together with the mind, do not enter into him — therefore, then, [this is called] silence (mauna).