Birth, death, living being and the whirligig.
Birth and death are but two stages in the journey of jiva,the living being in this whirligig called samsaara-samsarati iti samsaara- the living being keeps on moving.The living being is also called jiva. Mamaivaamso jivalokay jivabhooto sanaatanah-jiva is My own amsaa or fragment and is eternal.There was never a time when you were not there nor I was not there.You do not remember but I do-says Krishna to Arjuna in the Gita.
Living beings floating around in space are washed down by rain and fall in the fields,become a part of the food grains or other produce in the fields such as fruits,vegetables etc.When human beings or animals eat these foods,they become a part of their semen. During sexual intercourse the living being in the semen is lodged in the mothers womb.
The process of the growth of the living being and its gradual embodiment over a period of nine months is described in great detail in Srimad Bhagavatham.
Vedic mantras chanted at time of marriage as well as during the garbaadhaana ceremoney also beseech the Lord to give good progeny-satprajaa-to the couple.Over a period of nine months,the physical body,various limbs such as eyes,ears,hands,legs,skin,bones,marrow etc. are all produced in situation around the growing embriyo,which is all through fed thru the umbellical chord connecting the embriyo to the mother.Whatever the mother eats,child in the womb gets to partake. The pathetic travails of the child in the womb is described in the Bhagavatha, in the girbha stuti ,where it prays for the cessation of these travails,not being able to bear it any longer,and vowing never to return to the womb and asking the Lord’s help in making that happen.
When the gross body along with all appurtenances is ready around the jiva,with all hardware necessary for the different systems such as sensory,circulatory,pneumatic,digestive,blood,locomotion etc ,then the time for launch arrives.A team led by Purusha,the form of Supreme Lord,resident in every body,consisting of Mukhya Purana,Indra,Chandra,Surya,Varuna and other devatas presiding over the different senses,enter the womb,take up positions in their designated stations and take charge of the various functions.
Aiteriyopanishad has a beautiful description of how the stations of udara(stomach),hridaya(heart) and chorus(head)are created.
Finally the prasooti vaayu pushes out the child from the womb and the child comes out head first on the bed of the mother,and the umbellical chord connecting the mother to the child is chopped off.
This in short is birth.The child now forgets the travails of the residence in the womb and the vow that it took while in the womb.It is now ready to take field in its umpteenth innings as a human being.