CC Madhya 16.237
krame krame pāya loka bhava-sindhu-kūla
As stated in Śrīmad-Bhāgavatam (10.14.58):
samāśritā ye pada-pallava-plavaṁ
mahat-padaṁ puṇya-yaśo murāreḥ
bhavāmbudhir vatsa-padaṁ paraṁ padaṁ
padaṁ padaṁ yad vipadāṁ na teṣām
This material world is just like a big ocean. It begins with Brahmaloka and extends to Pātālaloka, and there are many planets, or islands, in this ocean. Not knowing about devotional service, the living entity wanders about this ocean, just as a man tries to swim to reach the shore. Our struggle for existence is similar to this. Everyone is trying to get out of the ocean of material existence. One cannot immediately reach the coast, but if one endeavors, he can cross the ocean by Śrī Caitanya Mahāprabhu’s mercy. One may be very eager to cross this ocean, but he cannot attain success by acting like a madman. He must swim over the ocean very patiently and intelligently under the instructions of Śrī Caitanya Mahāprabhu or His representative. Then, one day, he will reach the shore and return home, back to Godhead.