The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
13. On account of his being designated as the object of sight (the highest Self is meant, and) the same (is meant in the passage speaking of the meditation on the highest person by means of the syllable Om).
(In Pra. Up. V, 2) the general topic of discussion is set forth in the words, 'O Satyakâma, the syllable Om is the highest and also the other Brahman; therefore he who knows it arrives by the same means at one of the two.' The text then goes on, 'Again, he who meditates with this syllable Om of three mâtrâs on the highest Person,' &c.--Here the doubt presents itself, whether the object of meditation referred to in the latter passage is the highest Brahman or the other Brahman; a doubt based on the former passage, according to which both are under discussion.
The pûrvapakshin maintains that the other, i.e. the lower
Brahman, is referred to, because the text promises only a reward limited by a certain locality for him who knows it. For, as the highest Brahman is omnipresent, it would be inappropriate to assume that he who knows it obtains a fruit limited by a certain locality. The objection that, if the lower Brahman were understood, there would be no room for the qualification, 'the highest person,' is not valid, because the vital principal (prâna) may be called 'higher' with reference to the body 1.
To this we make the following reply: What is here taught as the object of meditation is the highest Brahman only.--Why?--On account of its being spoken of as the object of sight. For the person to be meditated upon is, in a complementary passage, spoken of as the object of the act of seeing, 'He sees the person dwelling in the castle (of the body; purusham purisayam), higher than that one who is of the shape of the individual soul, and who is himself higher (than the senses and their objects).' Now, of an act of meditation an unreal thing also can be the object, as, for instance, the merely imaginary object of a wish. But of the act of seeing, real things only are the objects, as we know from experience; we therefore conclude, that in the passage last quoted, the highest (only real) Self which corresponds to the mental act of complete intuition 2 is spoken of as the object of sight. This same highest Self we recognise in the passage under discussion as the object of meditation, in consequence of the term, 'the highest person.'--But--an objection will be raised--as the object of meditation we have the highest person, and as the object of sight the person higher than that one who is himself higher, &c.; how, then, are we to know that those two are identical?--The two passages, we
reply, have in common the terms 'highest' (or 'higher,' para) and 'person.' And it must not by any means be supposed that the term gîvaghana 1 refers to that highest person which, considered as the object of meditation, had previously been introduced as the general topic. For the consequence of that supposition would be that that highest person which is the object of sight would be different from that highest person which is represented as the object of meditation. We rather have to explain the word gîvaghana as 'He whose shape 2 is characterised by the gîvas;' so that what is really meant by that term is that limited condition of the highest Self which is owing to its adjuncts, and manifests itself in the form of gîvas, i e. individual souls; a condition analogous to the limitation of salt (in general) by means of the mass of a particular lump of salt. That limited condition of the Self may itself be called 'higher,' if viewed with regard to the senses and their objects.
Another (commentator) says that we have to understand by the word gîvaghana' the world of Brahman spoken of in the preceding sentence ('by the Sâman verses he is led up to the world of Brahman'), and again in the following sentence (v. 7), which may be called 'higher,' because it is higher than the other worlds. That world of Brahman may be called gîvaghana because all individual souls (gîva) with their organs of action may be viewed as comprised (sanghâta = ghana) within Hiranyagarbha, who is the Self of all organs, and dwells in the Brahma-world. We thus understand that he who is higher than that gîvaghana, i. e. the highest Self, which constitutes the object of sight, also constitutes the object of meditation. The qualification, moreover, expressed in the term 'the highest person' is in its place only if we understand the highest Self to be meant. For the name, 'the highest person,' can be given only to the highest Self, higher than which there is nothing. So another scriptural passage also says, 'Higher than the person there is nothing--this is the goal, the highest road.' Hence the
sacred text, which at first distinguishes between the higher and the lower Brahman ('the syllable Om is the higher and the lower Brahman'), and afterwards speaks of the highest Person to be meditated upon by means of the syllable Om, gives us to understand that the highest Person is nothing else but the highest Brahman. That the highest Self constitutes the object of meditation, is moreover intimated by the passage declaring that release from evil is the fruit (of meditation), 'As a snake is freed from its skin, so is he freed from evil.'--With reference to the objection that a fruit confined to a certain place is not an appropriate reward for him who meditates on the highest Self, we finally remark that the objection is removed, if we understand the passage to refer to emancipation by degrees. He who meditates on the highest Self by means of the syllable Om, as consisting of three mâtrâs, obtains for his (first) reward the world of Brahman, and after that, gradually, complete intuition.
172:1 Pindah sthûlo dehah, prânah sûtrâtmâ. Ânanda Giri.--The lower Brahman (hiranyagarbha on sûtrâtman) is the vital principle (prâna) in all creatures.
172:2 Samyagdarsana, i.e. complete seeing or intuition; the same term which in other places--where it is not requisite to insist on the idea of 'seeing' in contradistinction from 'reflecting' or 'meditating'--is rendered by perfect knowledge.
173:1 Translated above by 'of the shape of the individual soul.'
173:2 Pânini III, 3, 77, 'mûrttam ghanah.'