भूतग्रामः स एवायं भूत्वा भूत्वा प्रलीयते।
रात्र्यागमेऽवशः पार्थ प्रभवत्यहरागमे।।8.19।।
8.19 O son of Prtha, after being born again and again, that very multitude of beings disappears in spite of itself at the approach of night. It comes to life at the approach of day.
8.19 The same multitude of beings, controlled by Karma, evolves again and again, undergoing dissolution at the coming of night. Again at the coming of the day it comes forth. Similarly, at the end of the life span of Brahma which consists of a hundred years of three hundred and sixty days each, each Brahma-day being a thousand Caturyugas, all the worlds including that of Brahma and Brahma himself dissolve into Me in accordance with the order thus described in the Srutis: The earth is dissolved into the waters, the waters are dissolved into light etc., (Su. U., 2). The process of involution ends, after passing through all the other stages of dissolution, with the Avyakta, Akasa and Tamas. Therefore, for every other entity except Myself, origination and annihilation are unavoidable. So for those who seek Aisvarya (prosperity and power) birth and dissolution according to the above mentioned time arrangement are unavoidable. But in the case of those who attain to Me, there is no return again to Samsara. [The immense duration of time, according to ancient thinkers, is as follows: Catur-yuga, or a unit of the four yugas of Krta, Treta, Dvapara and Kali, has a cumulative duration of 4,320,000 human years. A thousand such periods constitute a day time of Brahma and a similar period his night. Periodic creation and dissolution of the universe take place in these two periods respectively. One year of Brahma consists of 360 such diurnal period. A Brahma has a life-span of 100 such years - i.e., 311, 040, 000,000,000 human years. At the end of it, there is a Mahapralaya, and a new Brahma comes into being. Time thus goes on endlessly]. Now Sri Krsna teaches that there is no return to Samsara even for those who have attained Kaivalya (isolation of the self).
Bhootagraamah sa evaayam bhootwaa bhootwaa praleeyate; Raatryaagame’vashah paartha prabhavatyaharaagame.
bhūta-grāmaḥ—the multitude of beings; saḥ—these; eva—certainly; ayam—this; bhūtvā bhūtvā—repeatedly taking birth; pralīyate—dissolves; rātri-āgame—with the advent of night; avaśhaḥ—helpless; pārtha—Arjun, the son of Pritha; prabhavati—become manifest; ahaḥ-āgame—with the advent of day