The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
23. (The stories told in the Upanishads) are for the purpose of the pâriplava; we deny this on account of (certain stories only) being specified.
'Yâgñavalkya had two wives, Maitreyî and Kâtyâyani' (Bri. Up. IV, 5, 1); 'Pratardana, forsooth, the son of Divodâsa came to the beloved abode of Indra' (Kau. Up. III, 1); 'There lived once upon a time Gânasruti Pautrâyana, who was a pious giver, giving much and keeping open house' (Kh. Up. IV, 1, 1); with regard to these and similar stories met with in the Vedânta portions of scripture there arises a doubt whether they are meant to subserve the performance of the pâriplava 1, or to introduce the vidyâs standing in proximity to them.
The pûrvapakshin maintains that those scriptural stories subserve the pâriplava because they are stories like others, and because the telling of stories is enjoined for the pâriplava. And from this it follows that the Vedânta-texts do not chiefly aim at knowledge, because like mantras they stand in a complementary relation to sacrificial performances.
This conclusion we deny 'on account of the specification.' Under the heading 'he is to recite the pâriplava,' scripture specifies certain definite stories such as that of 'Manu Vivasvat's son the king.' If, now, for the reason that all tales as such are alike, all tales were admitted for the pâriplava, the mentioned specification would be devoid of meaning. We therefore conclude that those scriptural stories are not meant to be told at the pâriplava.
305:1 I.e. have to be recited at stated intervals during the year occupied by the asvamedha sacrifice.