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.

Bhagavad Gita Verse 14, Chapter 3

annaadbhavanti bhootaani parjanyaadannasambhavaha |
yajnaadbhavati parjanyo yajnah karmasamudhbhavaha || 14 ||
 
From food are all beings created, from rain, food is created. Yajna gives birth to rain, and rain is born out of action.
 
annaat : from food
bhavanti : is created
bhootaani : all beings
parjanyaat : from rain
anna : food
sambhavaha : is created
yajnaad : from yajna
bhavati : is created
parjanyah : rain
yajnah : yajna
karmasamudhbhavaha : is created from action
 
Shri Krishna illustrates how yajna is embedded within the fabric of the entire universe. If we interpret this shloka literally, it refers to Vedic rituals that were used to invoke the rain-gods. But if we want to go deeper, we have to interpret this shloka symbolically.
 
We have seen that action is an integral tendency of any object in the universe. Even a tiny atom is always acting. So when any group of organisms - plants, animals, humans - collectively work for the sake of a higher ideal, that is called yajna. The output of this yajna is an environment that is charged with the potential to create almost anything. This environment is symbolically called "rain" in this shloka. Finally, this rain or productive potential creates all kinds of objects that are useful to organisms. The shloka refers to these objects as "food".
 
For instance, take a largely unknown area in northern California during World War II. Many scientists, lawyers, professors, business people came to this area with a higher ideal : to further the frontier of technology. Through their collective efforts, they created an environment which became conducive to technological innovation, which we now know as silicon valley. And silicon valley, even to this day, produces cutting edge products that benefit people around the world.
 
There are several such examples of environments born out of yajna: India's freedom struggle, the economic success of Singapore, the entertainment industry in Bombay and so on.
 
So the message here is that if people come together to work towards a higher ideal, it is a guarantee that their efforts will be successful.