MI.U 1.01

eṣa panthā etat karma etad brahma etat satyam। tasmān na pramādyet tam na atīyāt janah hi atyāyan pūrve। ye atyāyan te parābabhūvuḥ॥

This is the path, this is the action, this is Brahman, this is truth. Therefore, one should not be negligent, nor should one overstep it; for those who overstepped before, they perished.

tad uktam ṛṣiṇā -

That which was spoken by the sage -

prajā ha tisro atyāyamīyur-nyā arkam-abhito viviśre। bṛhadd tasthau bhuvaneṣv-antaḥ pavamāno harita āviveśeti।

Indeed, three offspring have moved downwards, other three have transcended and entered towards the Lord Arka from all sides. The great one stood within the worlds; the purifying Pavamāna, the one who carries, has thus entered.

prajā ha tisro atyāyamīyuranti yā vai tā imāḥ prajāstisro atyāyamāyaṃstānīmāni vayāṃsi vaṅgā vagadhāścerapādāḥ.

Indeed, three groups of offspring have migrated beyond; beyond the three offspring — namely, these tribes: the Vangas (the curved ones), the Vagadhas (sensually and materially driven), and the Cerapadas (violent, lawless).

nyanyā arkamabhito viviśra iti tā imāḥ prajā arkamabhito niviṣṭā imam evāgnim.

Thus, by another path, those creatures entered around Lord Arka; these creatures are settled around Lord Arka, which is indeed this Agni.

bṛhadd tasthau bhuvaneṣvantariti āda u eva bṛhad bhuvaneṣvantarasāvādityaḥ। pavamāno haranti āviviśeti vāyureva pavamāno diśo haranti āviṣṭaḥ॥1॥

Thus, the great one stood within the worlds; at the beginning, indeed, only the great one within the worlds, that is the Lord Aditya. The purifying one, Pavamāna carries (things), having entered; the wind itself is the purifying one, the directions carry (things), having entered.

MI.Bāshya 1.01

A testimonial from Rig Saṁhitā is quoted, providing the context in which the Aitareyī Upanishad teachings were revealed to Bahvṛca seer. This knowledge came directly from Lord Vishnu to Goddess Lakshmi, from her to Lord Brahma, and then to the rest of the gods.
The stated path here refers to the path that takes one directly to the Supreme Lord, who is eternally the source of action, the mother, the agent, being full of qualities, the truth, and the cause of one's own attainment. One should never forget Him anywhere - is the path.
The three types of beings who are after righteousness, knowledge, and dispassion, transcend and reach Lord Vishnu within the Sun, who is also called 'Arka' and 'Aditya'. They are purified by Pavamāna, the Lord Vishnu within the wind god, through renunciation of action and self-study. Those who are after wealth and sovereignty are lower beings bound to earth. 'Vayāṃsi' - those who abandon things or meat eaters, also known as 'Piśācas'; 'Vangas' - that which is curved or bent, i.e. crucked minded; 'Vagadhāḥ' - sensually driven, materially attached; 'Cerapādāḥ' - Violent, lawless, and disruptive.

"prādurbabhūva bhagavāṁstapasetarāyā nārāyaṇo'bhjajasutasya viśālāmnaḥ। tasmin gate'dhvaramabhūt suraviprasaṅgho niścetanastadanu padmabhavo'mumastaut॥

"The Lord Nārāyaṇa, distinct from the ascetic, became manifest for the son of the lotus-born, of Viśālāmnā. When he departed from the sacrifice, the assembly of gods and sages became unconscious. Then, the lotus-born (Brahmā) praised him.

tena stutaḥ sa bhagavān giriśendramukhyān sarvān abodhayad ajena sahaiva te’tha। dāsatvam āpurata eva mahatsurāṇāṃ dāsatvataḥ sa mahidāsa iti prasiddhaḥ॥

Having been praised by him, the Lord made all the foremost among the lords of mountains aware, together with Aja (Brahmā). Then, they indeed attained servitude to the great gods; from this servitude, he became well-known as Mahidāsa.

śṛṇvatsu teṣu bhagavān vadad ramāyai divyāṃ śrutiṃ sa paramo'timudaitareyīm। sā bahvṛcaiḥ prapaṭhitā caturānanāsyād yasyāṃ rahasyamuditaṃ paramaṃ hi viṣṇoḥ॥

While they were listening, the Lord, addressing Ramā, joyfully spoke the divine Aitareyī revelation. That revelation, recited by the Bahvṛca seers, originated from the mouth of the four-faced Brahmā, in which the supreme secret of Viṣṇu is indeed revealed.

mahābhūtiḥ śrutiḥ saiṣā mahābhūtir yato hariḥ। viśeṣeṇātra kathitaḥ sarvajñaḥ śāśvataḥ prabhuḥ॥"

This revelation is the great manifestation from whom Hari (the Lord) arises. Here, specifically, the omniscient, eternal Lord is described."

iti ṛk saṁhitāyām.

- stated thus, in the Ṛg Saṁhitā.

eṣa eva sadā "panthā" bhagavān puruṣottamaḥ। nityaṃ svaprāptihetutvāt kartṛtvāt karma mātṛtaḥ॥ brahmeṣa guṇapūrṇatvāt satyaṃ sādhu-svarūpataḥ। kvāpi taṃ vismarennaiva tyaktvā taṃ netaraṃ vrajet॥ pūrve nainaṃ tatyajurhi brahmādyāstena saṃsṛteḥ। muktāḥ śrīśca tadatyāgānnityamuktā guṇādhikāḥ॥

This indeed is always the very "path" — the Lord, the Supreme Person. Because He is eternally the cause of one's own attainment, the agent, the source of action, and the mother; this Brahman, being full of qualities, is truth and of virtuous nature. One should never forget Him anywhere, nor, having abandoned Him, go to another. The former ones, Brahma and others, indeed did not abandon Him, and by Him were liberated from transmigration. The liberated ones and Lakshmi, by never abandoning Him, are eternally liberated and superior in qualities.

vihāyasyayanāt proktā vayāṃsīti piśācakāḥ। vartitajñānato vaṅgā narāstairavanaṃ sadā॥

From the act of leaving and going, they are called 'vayāṃsi', the Piśācas; from the knowledge of conduct, the Vaṅgas, men by them always (inhabit) the earth.

annarūpairgṛdhnavo hi vaṅgāvgadha nāmakāḥ। rākṣasā asurā īrapādā iti samīritāḥ॥

Those greedy ones, taking such forms of food, are known as Vanga and Avagadha, and are called rākṣasas, asuras, and Cherapādas.

dharmo jñānaṃ ca vairāgyaṃ aiśvaryaṃ caturātmakaḥ। vāyur devo'trāsurāṇāṃ aiśvaryaṃ guṇa eva hi॥

Righteousness, knowledge, dispassion, and sovereignty are of a fourfold nature, and Vāyu is the deity here. Sovereignty and wealth alone are truly the qualities of deamons.

īrapādās tataḥ proktās te trayo viṣṇumaty ajan। parābhūtās tataḥ te tu tamasy andhe nipātitāḥ॥

Those swift-footed ones, thus spoken of, those three did not reach the mind established in Lord Vishnu. Defeated, therefore, they were cast down into utter darkness.

devāś ca ṛṣayo martyasattamā iti ca trayaḥ। āśritā viṣṇum evaikaṃ tristhānasthitam acyutam॥

The gods, the seers, and the best among mortals — these three have all taken refuge in Lord Viṣṇu alone, the one infallible being who abides in the three worlds.

agnisthamāśritā martyā viṣṇu markā bhidhaṃ param। ā janairarcitatvāt sa hyarka ityucyate hariḥ॥

Hari, who is Lord Viṣṇu, is situated in fire and is resorted to by mortals; because he is worshipped by people as the supreme, he is called Arka, the Sun.

agnau karmāṇi kṛtvaiva mānuṣā muktibhāginaḥ। karmabhiḥ śuddhasattvānāṃ karmatyāgo'pi nānyathā॥

Humans who perform actions in the fire indeed become eligible for liberation; for those whose essence is pure, renunciation of action is also only through actions, not otherwise.

āśritāḥ sūryagaṃ viṣṇum ṛṣayo bṛhad ity asau। tejasā bṛṃhaṇād ukto viṣṇur āditya ity api॥

The sages who go to the sun have resorted to Lord Viṣṇu and call him 'great'; thus, because of his brilliance and his power to increase, Viṣṇu is also called Āditya.

ādānāt sarvavastūnāṃ svādhyāyenāmumāśritāḥ। mucyanta ṛṣayo nityaṃ nānyathā tu kathaṃcana॥

By abstaining from taking all objects and resorting to self-study, sages are always liberated; never otherwise, in any way.

vāyusthamāśritā devāḥ pavamānābhidhaṃ harim। saṃsārāt pāvayitvā yat mahānande minotyayam॥

The gods, having taken refuge in Hari called Pavamāna, who is established in air, after being purified from saṃsāra, attain this one who measures (or grants) great bliss.

pavamānas tato viṣṇur vyāptaḥ sarvāsu dikṣu ca। āśrito bhagavān sarvaiḥ sarvatrāpi viśeṣataḥ॥ āśrayāt pṛthag ukto'yaṃ nityānando ramāpatiḥ॥

Thus, the purifying Lord Viṣṇu pervades all directions and is resorted to by all everywhere, especially; apart from the refuge, this Lord of Lakṣmī, who is eternal bliss, is said to be distinct.