Beginning His ten days of continual instruction to Rūpa Gosvāmī, Lord Śrī Caitanya Mahāprabhu said, "My dear Rūpa, the science of devotional service is just like a great ocean, and so it is not possible to show you its entire length and breadth. But I shall try to explain the nature of that ocean by taking just one drop out of it. In this way you can taste it and understand what that ocean of devotional service actually is."
The Lord then explained that within this brahmāṇḍa, or universe, there are innumerable living entities who, according to their own fruitive activities, are transmigrating from one species of life to another and from one planet to another. In this way their encagement in material existence has continued since time immemorial. In actuality, these living entities are atomic parts and parcels of the Supreme Spirit. It is said in the Śvetāśvatara Upaniṣad Śrīmad-Bhāgavatamthat the length and breadth of the individual soul is 1/10,000th part of the tip of a hair. The atomic magnitude of the living entity is confirmed in the Eleventh Canto of Śrīmad-Bhāgavatam (11.16.11).