Verse 2.17.1

पृथिवी हिंकारोऽन्तरिक्षं प्रस्तावो द्यौरुद्गीथो दिशः प्रतिहारः समुद्रो निधनमेताः शक्वर्यो लोकेषु प्रोताः ॥ २.१७.१ ॥

pṛthivī hiṃkāro'ntarikṣaṃ prastāvo dyaurudgītho diśaḥ pratihāraḥ samudro nidhanametāḥ śakvaryo lokeṣu protāḥ || 2.17.1 ||

1. The earth is the hiṃkāra, the space between the earth and heaven is the prastāva, heaven is the udgītha, the quarters are the pratihāra, and the ocean is the nidhana. The Sāma known as Śakvarī is rooted in the earth and other worlds.

Word-for-word explanation:

Pṛthivī hiṃkāraḥ, the earth is the hiṃkāra; antarikṣam prastāvaḥ, the space between the earth and heaven is the prastāva; dyauḥ udgīthaḥ, heaven is the udgītha; diśaḥ pratihāraḥ, the quarters are the pratihāra; samudraḥ nidhanam, the ocean is the nidhana; etāḥ śakvaryaḥ lokeṣu protāḥ, these [the Sāma called] Śakvarī are rooted in the earth and other worlds.

Commentary:

If the seasons come and go, as they ought to, then things on the earth and the other worlds remain in balance. This is why the Sāma is first worshipped as the seasons and then as the worlds.

But the question is: Sāma is singular. Why then has a plural word, śakvarī, been used here for the Sāma? Doesn’t it imply that there are many Sāmas? No, the Sāma is always one and the same. There are not many Sāmas. The word śakvarī has a plural form, but it stands for the singular Sāma. Śaṅkara gives the example of the word revatī, which is similarly always used in the plural.