Bhashya
रेव सशयमापन्न वरुण पितरमुपससार-अधीहि भगवो ब्रह्मेति ।क पुन ' सशयहेतुरस्येति, उच्यत-अन्नस्यात्पत्तिदर्शनात् ।तपस पुन पुनरुपदेश साधनातिशयत्वावधारणार्थ ।यावद्ब्रह्मणा लक्षण निरतिशय न भवति, यावच्च जिज्ञासा न निवर्तते, तावत्तप एव त साधनम्, तपसैव ब्रह्म विजिज्ञासस्वेत्यथ ।ऋज्वन्यत् ॥
In plain words
Having fallen into doubt, he approached his father Varuna once more with the plea: 'Teach me, O revered one, about Brahman.' What was the cause of his doubt? It is explained: because he observed that food itself has an origin. The repeated instruction to practice austerity is meant to establish its supreme efficacy as a spiritual tool. As long as the supreme definition of Brahman has not been fully grasped, and as long as the urge to inquire has not subsided, austerity alone remains the true instrument; through austerity alone you must seek to know Brahman—this is the purport. The rest is straightforward.
Close to the Sanskrit
Thus fallen into doubt, he approached Varuna the father: 'Teach, O venerable one, Brahman.' What again is the cause of his doubt? It is said: because of the observation of the origination of food. The repeated instruction of penance is for the purpose of ascertaining the supremacy of the means. As long as the definition by Brahman is not unsurpassed, and as long as the inquiry does not cease, so long austerity alone is that means; through austerity alone desire to know Brahman—this is the meaning. The rest is simple.