The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut [1896] at sacred-texts.com

10. (The direct statement is) non-comprehensive.

The direct scriptural statement implied in 'What a man does with knowledge' &c. does not refer to all knowledge, as it is connected with the knowledge forming the subject-matter of the section. And the latter is the knowledge of the udgîtha only, 'Let a man meditate on the syllable Om (as) the udgîtha.'