People do not know what is bhava-sāgara. They do not know even. But in Vedic literature, this is the first instruction, how to get out of this bhava-sindhu, bhava-sāgara, material ocean. The whole universe is also a ocean. And all these planets, they are called dvīpa. Just like this planet is called Jambudvīpa, Bhārata-varṣa. Actually it is like dvīpa. Nowadays, those who are flying in the sky, they're going from one island to another island, one planet to another planet. So when there is called dvīpa, there must be relative term, the ocean, or the sea. So whole this universe, this planets, they are called dvīpa. Therefore they are floating in the ocean of air. Just like you have got experience. You have got experience of this also, ocean of water. And above water, there is air, ocean of air. Then there is sky.
So bhava-sāgarasya. The whole universe is bhava-sāgara. Sāgara means ocean, or sea. And bhava means repetition of birth and death. Bhava. Bhūtvā bhūtvā pralīyate (BG 8.19), in the Bhagavad-gītā. Once we take birth, we remain here for some time, then we give up this body; we accept another body. Tathā dehāntara-prāptir dhīras tatra na muhyati (BG 2.13). We have to . . . so long we are in this material ocean, we have to accept these laws of nature, repetition of birth and death. This is called bhava-sāgara. So we are eternal, nityaḥ śāśvato 'yaṁ na hanyate hanyamāne śarīre (BG 2.20). It requires little intelligence that, "I am eternal. Why I am in this business, accepting one body and again giving up, giving it up? And there is no guarantee what kind of body I'm going to accept next." There is no guarantee. It will be according to your work. We can become an insect, or we can become the demigod. We can become tree; we can become animal—anything, according to our karma. karmaṇā daiva-netreṇa (SB 3.31.1).