The Lord creates the material world to give the conditioned souls a chance to elevate themselves to the higher platform of Kṛṣṇa consciousness. If a conditioned soul does not take advantage of this opportunity, after the dissolution of this material world he enters into the body of Nārāyaṇa and remains there in deep sleep until the time of another creation.
In this connection the example of the rainy season is very appropriate. Seasonal rainfall may be taken as the agent for creation because after the rainfall the wet fields are favorable for growing different types of vegetation. Similarly, as soon as there is creation by the Lord's glancing over the material nature, immediately the living entities spring up in their different living conditions, just as different types of vegetation grow after a rainfall. The rainfall is one, but the creation of the different plants is varied. The rain falls equally on the whole field, but the different plants sprout up in different shapes and forms according to the seeds planted. Similarly, the seeds of our desires are varied. Every living entity has a different type of desire, and that desire is the seed which causes his growth in a certain type of body. This is explained by Rūpa Gosvāmī by the word pāpa-bīja. Pāpa means "sinful." All our material desires are to be taken as pāpa-bīja, or the seeds of sinful desires. The Bhagavad-gītā explains that our sinful desire is that we do not surrender unto the Supreme Lord. The Lord therefore says in the Bhagavad-gītā, "I shall give you protection from the reactions of sinful desires." These sinful desires are manifested in different types of bodies; therefore, no one can accuse the Supreme Lord of partiality in giving one type of body to a certain type of living entity and another type of body to another living entity. All the bodies of the 8,400,000 species are created according to the mental condition of the individual living entities. The Supreme Personality of Godhead, Puruṣottama, only gives them a chance to act according to their desires. Therefore, the living entities act by taking advantage of the facility given by the Lord.