The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
22. And on account of the words expressive of becoming.
Moreover the text exhibits words of clearly injunctive meaning, in connexion with the passages quoted above, viz. 'Let him meditate on the udgîtha' (Kh. Up. I, 1, 1); 'Let him meditate on the Sâman' (Kh. Up. II, 2, 1); 'Let him think: I am the hymn' (Ait. Âr. II, 1, 6). Now these injunctive forms would be rendered futile by the assumption of the texts under discussion aiming at glorification only. Compare the following saying of those who know Nyâya, 'Let him do, let it be done, it is to be done, let it become, let it be; these forms are in all Vedas the settled signs of injunction.' What they mean thereby is that injunction is the sense of all potential, imperative, &c., verbal forms.--Moreover in each of the sections to which the passages under discussion belong the text states special fruits, 'He becomes indeed a fulfiller of desires' (Kh. Up. I, 1, 7); 'He is able to obtain wishes through his song' (Kh. Up. I, 7, 9); 'The worlds in an ascending and a descending line belong to him' (Kh. Up. II, 2, 3). For this reason also the texts
about the udgîtha and so on are meant to enjoin devout meditations.