The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
3. On account of scripture showing (certain lines of) conduct.
'Ganaka the king of the Videhas sacrificed with a sacrifice at which many presents were given to the priests' (Bri. Up. III, 1, 1); 'Sirs, I am going to perform a sacrifice' (Kh. Up. V, 11, 5); these and similar passages--which occur in sections that have another purport--show that those who know Brahman are connected with sacrificial action also. And similarly we apprehend from the fact that according to scripture Uddâlaka and others taught their sons and so on, that they were connected with the condition of life of householders. If mere knowledge could effect the purpose of man, why should the persons mentioned have perforated works troublesome in many respects? 'If a man would find honey in the Arka tree why should he go to the forest?'