Bhashya
व्याहृत्यात्मनो ब्रह्मण उपासनमुक्तम् ।अनन्तर चपाङ्क्तस्वरूपेण तस्यैवोपासनमुक्तम् ।इदानीं सर्वोपासनाङ्गभूतस्य ओंकारस्योपासनं विधित्स्यते ।परापरब्रह्म-ष्टव्या हि उपास्यमान ओंकार शब्दमात्रोऽपि परापरब्रह्मप्राप्तिसाधनं भवति , स ह्यालम्बनं ब्रह्मण परस्यापरस्य च,प्रतिमेव विष्णो , 'एतेनैवायतनेनैकतरमन्वति इति श्रुते ।ओमिति, इतिशब्द स्वरूपपरिच्छेदार्थ , ॐ इत्येतच्छब्द-रूप ब्रह्म इति मनसा धारयेत उपासीत, यत ॐ इतिइद सर्व हि शब्दस्वरूपमोकारेण व्याप्तम् , 'तद्यथा शङ्कुना'इति श्रुत्यन्तरात् ।'अभिधानतन्त्र ह्यभिधेयम् ' इत्यत इदसर्वमोकार इत्युच्यते ।ओकारस्तुत्यर्थ उत्तरो ग्रन्थ , उपा-स्यत्वात्तस्य ।ॐ इत्येतत् अनुकृति अनुकरणम् ।करोमियास्यामि चेति कृतमुक्त ओमित्यनुकरोत्यन्य , अत ओकारोऽनुकृति ।ह स्म वै इति प्रसिद्धार्थद्योतका ।प्रसिद्धह्योकारस्यानुकृतित्वम् ।अपि च ओश्रावय इति प्रैषपूर्वमा-श्रावयन्ति प्रतिश्रावयन्ति ।तथा ॐ इति सामानि गायन्तिसामगा ।ॐ शोमिति शस्त्राणि शसन्ति शस्त्रशसितारोऽपि ।तथा ॐ इति अध्वर्यु प्रतिगर प्रतिगृणाति ।ॐ इति ब्रह्माप्रसौति अनुजानाति ।ॐ इति अग्निहोत्रम् अनुजानाति जुहो-मीत्युक्त ॐ इत्यव अनुज्ञा प्रयच्छति ।ॐ इत्येव ब्राह्मणप्रवक्ष्यन प्रवचन करिष्यन् अध्येष्यमाण ओमित्याह ओ-मित्येव प्रतिपद्यते अध्येतुमित्यर्थ , ब्रह्म नेदम् उपाप्नवानिइति प्राप्नुया ग्रहीष्यामीति उपाप्नोत्येव ब्रह्म ।अथवा, ब्रह्मपरमात्मानम् उपाप्रवानीत्यात्मान प्रवक्ष्यन प्रापयिष्यन् ओमित्येवाह ।स च तेनोङ्कारेण ब्रह्म प्राप्नोत्येव ।ओकार-पूर्व प्रवृत्तानां क्रियाणां फलवत्त्वं यस्मात्, तस्मादोकारब्रह्मेत्युपासीतेति वाक्यार्थः ॥
In plain words
The meditation upon Brahman in the form of the vyāhṛtis has been explained, and subsequently the meditation upon that same Brahman through pentads. Now, the meditation upon the syllable Oṁ—which forms a limb of all meditations—is introduced. When meditated upon with regard to the higher and lower Brahman, the syllable Oṁ serves as the direct means to attain both. It is the support of Brahman, both higher and lower, functioning just like an idol of Viṣṇu, as confirmed by the scriptural passage: 'By this very support one attains one or the other.' The word 'Om' bounded by 'iti' indicates the exact form of the syllable; holding this sound-form in the mind, one should meditate upon it. Because this entire universe of names and forms is pervaded by the syllable Oṁ, just as all leaves are pierced by the stalk in another scriptural simile. Since the object designated is entirely dependent upon its designation, all this is indeed spoken of as Oṁ. The subsequent text serves to praise Oṁ, as it is the direct object of meditation. 'Om is imitation'—meaning that when someone says 'I will do this' or 'I will go,' another echoes it by saying 'Om'; hence Oṁ is an imitation or response. The particles 'ha sma vai' indicate well-known usage, for it is well known that Oṁ functions as an echo. Furthermore, in the ritual call 'Ośrāvaya,' preceded by a directive, the priests respond. With 'Om' the Sāman singers chant their hymns; with 'Om śom' the reciters chant the Śastras; with 'Om' the Adhvaryu gives his assent; with 'Om' the Brahmā priest grants permission; and with 'Om' the Agnihotra is sanctioned, for when the sacrificer says 'I am offering,' permission is granted with 'Om.' Similarly, a Brāhmaṇa about to commence his Vedic study says 'Om' and begins, meaning 'May I attain Brahman'—and he verily attains Brahman. Alternatively, intending to expound the Supreme Self, the teacher says 'Om,' and through that Oṁ the seeker attains Brahman. Because actions initiated with Oṁ bear fruit, one should meditate upon the syllable Oṁ as Brahman—this is the purport of the teaching.
Close to the Sanskrit
Meditation on vyāhṛti-natured Brahman has been stated. And subsequently meditation on that same in the form of pentads has been stated. Now the meditation on the syllable Oṁ, which constitutes a limb of all meditations, is desired to be prescribed—because when meditated upon with the view of higher and lower Brahman, the syllable Oṁ indeed becomes the means of attaining higher and lower Brahman. For it is the support of Brahman, both the higher and the lower, like an image of Viṣṇu. As the śruti says: 'By this very support one attains one or the other.' 'Om'—the word 'iti' is for the purpose of limiting the form; holding in the mind this sound-form called Oṁ, one should worship it. Because all this creation is indeed sound-form, pervaded by the syllable Oṁ, 'just as by a leaf-stalk' from another śruti text. For the object designated is dependent on the designation; hence all this is spoken of as the syllable Oṁ. The subsequent text is for the purpose of praising Oṁ, because it is an object of meditation. 'Om this is imitation'—imitation means: 'I do,' 'I will go,' thus when done and spoken, another imitates saying 'Om'; therefore Oṁ is imitation. 'Hā sma vai' are particles indicating well-known meaning; for it is well known that Oṁ has the nature of imitation. And also—'Ośrāvaya'—preceded by a directive, they cause to hear and respond. Thus with 'Om' Sāman singers sing Sāman chants. With 'Om śom' the Śastra reciters recite Śastras. Thus with 'Om' the Adhvaryu priest responds to the Pratigara. With 'Om' the Brahmā priest permits. With 'Om' he approves the Agnihotra—when 'I offer' is spoken, with 'Om' indeed he grants permission. With 'Om' indeed a Brāhmaṇa, about to recite, performing recitation, about to study, says 'Om', commences to study—meaning: 'May I attain Brahman'—attains Brahman indeed. Or else, 'May I attain the Supreme Self, Brahman,' about to expound, about to lead to the Self, says 'Om' indeed. And he by that Oṁ attains Brahman indeed. Since actions initiated with Oṁ bear fruit, therefore one should worship Oṁ as Brahman—this is the sentence meaning.