prakritim yanti mamikam
kalpa-ksaye punas tani
kalpadau visrjamy aham
O son of Kunti, at the end of the millennium all material manifestations enter into My nature, and at the beginning of another millennium, by My potency, I create them again.
Commentary by Srila Prabhupada
The creation, maintenance and annihilation of this material cosmic manifestation are completely dependent on the supreme will of the Personality of Godhead. “At the end of the millennium” means at the death of Brahma. Brahma lives for one hundred years, and his one day is calculated at 4,300,000,000 of our earthly years. His night is of the same duration. His month consists of thirty such days and nights, and his year of twelve months. After one hundred such years, when Brahma dies, the devastation or annihilation takes place; this means that the energy manifested by the Supreme Lord is again wound up in Himself. Then again, when there is a need to manifest the cosmic world, it is done by His will. Bahu syam: “Although I am one, I shall become many.” This is the Vedic aphorism (Chandogya Upanishad 6.2.3). He expands Himself in this material energy, and the whole cosmic manifestation again takes place.
Commentary by Sri Visvanatha Cakravarti Thakur
“I understand that all these things which can presently be seen are situated in you, but at the time of destruction where will they go?” This verse answers.
All these things will merge into my energy called prakrti composed of the three gunas. At the end of the period of destruction, at the time of creation, (kalpa ksaye), I will again create everything in detail (visesena srjami).