Avatarika
यस्य नेति नेतीत्यन्यप्रतिषेधद्वारेण ब्रह्मणो निर्देशःकृतः तस्य विधिमुखेन्न कथं निर्देशः कर्तव्य इति पुनरा-ख्यायिकामेवाश्रित्याह मूलं च जगतो वक्तव्यमिति ।आ-ख्यायिकासंबन्धस्त्वब्रह्मविदो ब्राह्मणाञ्जित्वा गोधनं हर्तव्य-मिति + न्याय्यं मत्वाइ--
In plain words
Brahman has already been pointed to by saying what it isn't — not this, not this. So doesn't it also deserve to be pointed to by saying what it is? That question is exactly why the text turns back to the story, and why it now has to name the root of the whole world. And here's why the story belongs here at all: the reasoning is that once someone who doesn't actually know Brahman is beaten in the contest, it's only fair that his cattle go to the one who won.
Close to the Sanskrit
Of that [Brahman] concerning which a designation has been made by way of negating everything else — [as in] 'not this, not this' — should a designation by way of positive injunction not also be made, and how? [Anticipating this], resorting once again to the story, the text states, and [also] that the root of the world must be stated. As for the story's connection [with the present topic]: it is introduced having judged it proper that, once Brahmins who do not know Brahman are defeated [in debate], their cattle-wealth should be taken —