Chapter 9, Verse 7

सर्वभूतानि कौन्तेय प्रकृतिं यान्ति मामिकाम्।
कल्पक्षये पुनस्तानि कल्पादौ विसृजाम्यहम्।।9.7।।

sarva-bhūtāni kaunteya prakṛitiṁ yānti māmikām
kalpa-kṣhaye punas tāni kalpādau visṛijāmyaham

sarva-bhūtāni — all living beings;
kaunteya — Arjun, the son of Kunti;
prakṛitim — primordial material energy;
yānti — merge;
māmikām — my;
kalpa-kṣhaye — at the end of a kalpa;
punaḥ — again;
tāni — them;
kalpa-ādau — at the beginning of a kalpa;
visṛijāmi — manifest;
aham — I

In this verse, Krishna is telling Arjuna that everything we see in the material world, like plants, animals, and even humans, has a cycle. Think of it like a very long movie. At some point, the movie gets to the end, and everything in that movie, all the characters and scenes, fade away. This moment is what Krishna calls the end of the millennium. It's like a big reset when everything goes back to its origin, which is Krishna himself.

Now, to put it in simpler terms, imagine a play in a theater. Once the performance is over, the stage is cleared, and everything goes back to the storage room. After a while, when it's time for another performance, the actors and the props come out again, and a new show begins. That's the beginning of another millennium.

Krishna explains that after a very long period, called a kalpa, everything we see returns to Him. He absorbs all the forms of life and material nature back into himself. But just like a play is resumed with the same actors and props, at the start of a new kalpa, Krishna, with his supreme power, brings everything back into existence.

The part about Brahma living for a hundred of his years also shows us how large the time scales are in this idea. Brahma's life is extraordinarily long when compared to our human years.

So, what this verse tells us is that there is a continuous cycle of creation and destruction, all controlled by Krishna's will. He is the source of everything, and when the time is right, He brings the universe back into being, just as he did before. We are all part of this huge cycle, and while our lives may seem important, they are just one small part of this ongoing process of creation, preservation, and dissolution.