Verse 1.3.1

अथाधिदैवतं य एवासौ तपति तमुद्गीथमुपासीतोद्यन्वा एष प्रजाभ्य उद्गायति । उद्यंस्तमो भयमपहन्त्यपहन्ता ह वै भयस्य तमसो भवति य एवं वेद ॥ १.३.१ ॥

athādhidaivataṃ ya evāsau tapati tamudgīthamupāsītodyanvā eṣa prajābhya udgāyati | udyaṃstamo bhayamapahantyapahantā ha vai bhayasya tamaso bhavati ya evaṃ veda || 1.3.1 ||

1. Next, how you worship from the standpoint of the forces of nature: There is the sun rising to give us heat. Worship it as udgītha. The sun rises to pray, as it were, for the welfare of all living beings. As it rises, it dispels the fear of darkness. One who knows this overcomes the fear of ignorance about birth and death.

Word-for-word explanation:

Atha, next; adhidaivatam, relating to the elements [such as rain, lightning, and other forces of nature]; yaḥ eva asau, that [i.e., the sun] over there which; tapati, gives us heat; tam, to that; udgītham upāsīta, worship as udgītha; udyan, as it rises; vai eṣaḥ, this [sun]; prajābhyaḥ, for all living beings; udgāyati, [as if] it prays for their well-being; udyan, as [the sun] rises; tamaḥ bhayam apahanti, it removes the fear of darkness; yaḥ, one who; evam veda, knows this; vai bhayasya, the fear [of birth and death]; tamasaḥ, ignorance; apahantā bhavati, overcomes.

Commentary:

There are many ways of using udgītha as worship. This verse gives an example of how you use it in worshipping the forces of nature (adhidaivata). There is the sun above giving us heat. The Upaniṣad says to worship udgītha as the sun. But if udgītha is Om, how can it stand for the sun? The sun helps the plants, such as paddy, to grow. Without the sun, life on this planet would be impossible. It is as if the sun sings the udgītha for us to sustain us. This is why the sun is referred to as the udgītha. As udgītha, the sun also dispels our fear of darkness.

One who knows this is no longer afraid of birth and death. That is, he knows he is immortal.