Bhagavad Gita Verse 3, Chapter 14

mama yonirmahadbrahma tasmingarbham dadhaamyaham |
sambhavaha sarvabhootaanaam tato bhavati bhaarata || 3 ||
 
My womb is the great brahman. In it, I place the seed. From that, O Bharaata, is the birth of all beings.
 
mama : my
yonihi : womb
mahadbrahma : great brahman
tasmin : in it
garbham : seed
dadhaami : place
aham : I
sambhavaha : birth
sarvabhootaanaam : all beings
tataha : from that
bhavati : happens
bhaarata : O Bhaarata
 
According to the theory of karma, each jeeva or individual soul generates new unfulfilled desires or vaasanaas. These vaasanaas are created as a result of karma phala or fruits of action. Each action of eating a sweet creates a new desire to eat a sweet later, for instance. One lifetime is not enough to exhaust these vaasanaas, causing the jeeva to continuously take birth in the world to fulfill its desires. This is the explanation of birth and rebirth of jeevas. But how does the universe itself begin? Shri Krishna describes this topic in extremely poetic language in two shlokas.
 
Ishvara, at the beginning of creation, splits himself into his two aspects. One aspect is Prakriti, referred to here as the "great brahman", which comprises three gunaas or qualities. Prakriti has the power to generate an infinite variety of forms through innumerable permutations and combinations of its three gunaas. But it is inert. It cannot create the universe by itself. The awareness aspect of Ishvara, the kshetrajnya, is needed to infuse Prakriti with life. This happens when Ishvara places all of the jeevas into Prakriti, just like seeds are placed into soil.
 
Let’s examine this in more detail. How exactly does the jeeva come into contact with Prakriti? It is due to avidyaa or ignorance. Each jeeva’s vaasanaas or unfulfilled desires are caused by its ignorance of its true nature which is infinite. Instead, the jeeva, also known as the Purusha, thinks that it is incomplete, and mistakenly rushes out into Prakriti to make itself complete again. This illusory link between the Purusha and Prakriti becomes the source of its birth and rebirth in the cycle of samsaara.