। ॥ ४५ ॥
In plain words
It leans on nothing else, and every instrument of knowing leans on it: the word of the Veda. Where Brahman is to be known — and whatever else lies past the reach of the senses — that word is the measure.
Close to the Sanskrit
That which does not depend on anything else, and which all the means of knowledge depend upon — that statement of the Vedas is the means of knowledge in the apprehension of Brahman and the other things beyond the senses.