Bhashya
एष उ एव प्रकृत आङ्गिरसो बृहस्पतिः ।कथं बृहस्पति-रिति, उच्यते— वाग्वै बृहती बृहतीच्छन्दः षट्त्रिंशद-क्षरा ।अनुष्टुप् च वाक् ; कथम् ? ‘वाग्वा अनुष्टुप्’ इतिश्रुतेः ; सा च वागनुष्टुब्बृहत्यां छन्दस्यन्तर्भवति ; अतोयुक्तम् ‘वाग्वै बृहती’ इति प्रसिद्धवद्वक्तुम् ।बृहत्यां च सर्वाऋचोऽन्तर्भवन्ति, प्राणसंस्तुतत्वात् ; ‘प्राणो बृहती प्राणऋच इत्येव विद्यात्’ इति श्रुत्यन्तरात् ; वागात्मत्वाच्चर्चांप्राणेऽन्तर्भावः ; तत्कथमित्याह— तस्या वाचो बृहत्याऋचः, एषः प्राणः, पतिः, तस्या निर्वर्तकत्वात् ; कौष्ठ्या-ग्निप्रेरितमारुतनिर्वर्त्या हि ऋक् ; पालनाद्वा वाचः पतिः ;प्राणेन हि पाल्यते वाक्, अप्राणस्य शब्दोच्चारणसामर्थ्या-भावात् ; तस्मादु बृहस्पतिः ऋचां प्राण आत्मेत्यर्थः ॥
In plain words
This very entity is the Āṅgirasa Bṛhaspati under discussion. How is he called Bṛhaspati? The text explains: Speech is indeed the Bṛhatī meter, consisting of thirty-six syllables. Anuṣṭubh is also speech; how so? Because of the Vedic passage, 'Speech indeed is Anuṣṭubh.' That speech-Anuṣṭubh is included within the Bṛhatī meter, which is why it is fitting to declare proverbially that 'Speech is indeed Bṛhatī.' Furthermore, all Ṛg hymns are contained within Bṛhatī because they are praised in connection with Prana, as another scriptural passage states: 'One should know Prana alone as Bṛhatī, and Prana as the Ṛg hymns.' Because speech is essentially Prana, the Ṛg hymns naturally find their resting place in Prana. How does this work? The text clarifies: Of those Ṛg hymns belonging to speech as Bṛhatī, this Prana is the lord, because he brings them into manifestation. For a Ṛg hymn is articulated by the breath driven by the inner gastric fire. Alternatively, 'lord' can mean protector; speech is indeed protected by Prana, since without Prana there is no capacity to utter sound. Therefore, Bṛhaspati means that Prana is the true Self of the Ṛg hymns.
Close to the Sanskrit
This same one is the Aṅgirasa Bṛhaspati under discussion. How is he Bṛhaspati? It is spoken: speech indeed is the Bṛhatī meter, having thirty-six syllables. Anuṣṭubh is also speech; how? From the scriptural text 'Speech indeed is Anuṣṭubh'; and that speech-Anuṣṭubh is included within the Bṛhatī meter; hence it is appropriate to speak of 'Speech indeed is Bṛhatī' as something well-known. And all Ṛg hymns are included within Bṛhatī, because of being praised with Prana; from another scriptural text 'One should know Prana alone as Bṛhatī, Prana as the Ṛg hymns'; and because of speech having the nature of Prana, the inclusion of the Ṛg hymn in Prana. How is that? He says— of that speech which is Bṛhatī, the Ṛg hymns, this Prana is the lord, because of being their accomplisher; for a Ṛg hymn is accomplished by the wind impelled by the gastric fire; or because of the protection of speech; for speech is protected indeed by Prana, because of the absence of the capacity to pronounce sound in that which lacks Prana; therefore Bṛhaspati means that Prana is the Self of the Ṛg hymns.