The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
REVERENCE TO THE HIGHEST SELF!
1. Repetition (of the mental functions of knowing, meditating, &c., is required) on account of the text giving instruction more than once.
The third adhyâya was taken up chiefly with a discussion of the means of knowledge as related to the higher and lower vidyâs. In the fourth adhyâya we shall now discuss the fruits of knowledge, and as occasion suggests some other topics also.--In the beginning, however, we shall carry on, in a few adhikaranas, a special discussion connected with the means of knowledge. 'Verily the Self is to be seen, to be heard, to be thought, to be reflected on' (Bri. Up. II, 4, 5); 'Let a wise Brâhmana after he has discovered him practise wisdom' (Bri. Up. IV, 4, 21); 'That it is which we must search out, that it is which we must try to understand' (Kh. Up. VIII, 7. 1).
Concerning these and similar passages a doubt arises whether the mental action referred to in them is to be performed once only or repeatedly.--Once only, the pûrvapakshin says; as in the case of the prayâga-offerings and the like. For thereby the purpose of scripture is accomplished; while to practise repetitions not demanded by scripture would be to accomplish what is not the purpose of scripture.--But passages have been quoted which teach repetition 'it is to be heard, to be thought, to be reflected on,' &c.!--Let us then repeat exactly as scripture says, i.e. let us hear the Self once, let us think it once, let us reflect on it once, and nothing more. But where scripture teaches something once only--viz. in such passages as 'He knows,' 'Let him meditate,' &c.--no repetition has to be practised.--To this we reply as
follows. Repetition is to be performed because scripture gives repeated instruction. For the repeated instruction contained in passages such as 'He is to be heard, to be thought, to be reflected on' intimates the repetition of the required mental acts.--But the pûrvapakshin has said above that the repetition is to extend exactly to what scripture says and not to go further!--This is wrong, we reply, because all those mental activities have for their end intuition. For hearing and so on when repeated terminate in intuition, and thus subserve a seen purpose, just as the action of beating. &c., terminates in freeing the rice grains from their husks. Moreover also such terms as 'meditating,' 'being devoted to,' and 'reflecting 'denote actions in which repetition is implied as a quality. Thus we say in ordinary life that a person 'is devoted' to a teacher or a king if he follows him with a mind steadily set on him; and of a wife whose husband has gone on a journey we say that she thinks of him, only if she steadily remembers him with longing. And (that also 'knowing' implies repetition, follows from the fact that) in the Vedânta-texts the terms 'knowing' and 'meditating' are seen to be used one in the place of the other. In some passages the term 'knowing' is used in the beginning and the term 'meditating' in the end; thus e.g. 'He who knows what he knows is thus spoken of by me,' and: Teach me, sir, the deity which you meditate on' (Kh. Up. IV, 1, 4; 2, 2). In other places the text at first speaks of 'meditating' and later on of 'knowing;' thus e.g. 'Let a man meditate on mind as Brahman,' and 'He who knows this shines and warms through his celebrity, fame, and glory of countenance' (Kh. Up. III, 18, 1; 6).--From this it follows that repetition has to be practised there also, where the text gives instruction once only. Where, again, the text gives repeated instruction, repeated performance of the mental acts is directly intimated.