Why there are different types of bodies? Because you wanted a particular type of enjoyment under the influence of material nature. As already explained, there are three material nature quality—sattva-guṇa, rajo-guṇa, tamo-guṇa. Now, we mix them. Three into three, it becomes nine. And nine multiplied by nine, it becomes eighty-one. Therefore there are 8,400,000 species of life, according to the material quality. That is explained here. Puruṣaḥ prakṛti-stho hi bhuṅkte prakṛti-jān guṇān (BG 13.22). Prakṛti-jān guṇān. To possess different types of body means to satisfy different types of desires, under the influence of the modes of material nature. Full freedom. Therefore when one is advanced in consciousness, he doesn't want to enjoy anything of this material world, any way. He doesn't desire either to become the king or Lord Brahmā or the stool, or, I mean to say, the worms of the stool.
These are the different varieties. Jalajā nava-lakṣāṇi sthāvarā lakṣa-viṁśati (Padma Purāṇa). According to our desire we get body. In the water, nine hundred thousand forms. Similarly, in the botanical garden, they have given signboard, "This is this, this is this." But there are two millions types of trees and plants. How many they know? Two million. If you search out through the whole botanical garden, hardly you will find two thousand, three thousand species. Or even find ten thousand. Still, what it is? There are two millions. Jalajā nava-lakṣāṇi sthāvarā lakṣa-viṁśati. This is knowledge.
So if we read the Vedic literature, and you get full knowledge, and the essence of Vedic literature is Śrīmad-Bhāgavatam. And the Bhagavad-gītā is the preliminary study of Śrīmad-Bhāgavatam, A-B-C-D. This Bhagavad-gītā is the A-B-C-D of knowledge. This is entrance examination, matriculation examination, school-leaving examination. And Śrīmad-Bhāgavata is graduate. When you become graduate in spiritual knowledge, then you can understand Śrīmad-Bhāgavatam. And when you have passed your Bachelor degree, when you are postgraduate, that study is Śrī-Caitanya-caritāmṛta.