Verse 3.13.1

तस्य ह वा एतस्य हृदयस्य पञ्च देवसुषयः स योऽस्य प्राङ्सुषिः स प्राणस्तच्चक्षुः स आदित्यस्तदेतत्तेजोऽन्नाद्यमित्युपासीत तेजस्व्यन्नादो भवति य एवं वेद ॥ ३.१३.१ ॥

tasya ha vā etasya hṛdayasya pañca devasuṣayaḥ sa yo'sya prāṅsuṣiḥ sa prāṇastaccakṣuḥ sa ādityastadetattejo'nnādyamityupāsīta tejasvyannādo bhavati ya evaṃ veda || 3.13.1 ||

1. In the heart there are five doors guarded by the gods. The door in the east is prāṇa. It is also the eyes, and it is Āditya. Worship this as the source of brightness and food. He who knows this becomes bright and enjoys food.

Word-for-word explanation:

Tasya ha vai etasya hṛdayasya, of this heart; pañca devasuṣayaḥ, five passages guarded by the gods; saḥ yaḥ, that which; asya prāṅsuṣiḥ, is its eastern passage; saḥ prāṇaḥ, that is prāṇa; tat cakṣuḥ, that is [also] the eye; saḥ ādityaḥ, [and] that is Āditya [the sun]; tat etat, it is that; tejaḥ annādyam iti upāsīta, meditate on as the source of brightness and food; yaḥ evam veda, he who knows this; tejasvī annādaḥ bhavati, becomes bright and an eater of food.

Commentary:

If you want to enter a house, you must please those who are at the gates. Similarly, if you want to enter heaven, you must worship Brahman as prāṇa. As you do so, you should attribute to prāṇa the qualities of Àditya and annāda—that is, of brightness and strength. If. prāṇa is pleased with you, you have no difficulty attaining heaven.