The God is said to be the ‘Supreme’ spiritual entity that is eternal, infinite, formless and boundless. One who is supreme cannot be said to be supreme if there is someone who is even superior to him. And the mother is, no doubt superior to the child she gives birth to. This is called ‘Matri-Rin’ or ‘debt’ and this is such a debt which can never be repaid and an indebted person cannot be said to be ‘Supreme’!
So the whole concept of being ‘supreme’ would be shattered if there is or has been anyone who is or has been superior to the ‘supreme’ entity.
This is one way of explaining why God is unborn because he is second to no one. He is eternal which means ‘Sanatan‘ i.e. ever existing. In Gita the word ‘eternal’ or ‘ sanatan’ has been used for the God Head, the Creation or ‘Srishti’, Soul or ‘Atma’, Knowledge or ‘Gyan’, the sound of existence I.e ‘Om‘ or ‘Omkara‘ and Samaya (Kaal). So, all these terms are synonyms of the God Head himself.
Another way of explaining why God is unborn is rather complicated. There are two kinds of World or Universes in the nature. One is ‘Spiritual’ and the other is ‘Material’. The world in which we are living is called the material world.
There are many more material worlds in the nature. In fact, whatever we can see or perceive through our senses is included in this category. We can see the sun, moon, stars and planets etc. so all these are material worlds indeed. The highest one is said to be the ‘Brahmand’, which is headed by Lord Brahma himself.
Much beyond the end of the territory of the material worlds (say millions and millions miles ahead) is another world called ‘Spiritual World’ which is the abode of the God Head.
The basic difference between these two worlds is that the living beings of the material world have a body and are mortal and subject to the miseries attached to the birth, old age, disease and death etc. but the living beings of the spiritual world are immortal, eternal, infinite and formless i.e. ‘Nirakar‘.
The relationships of father, mother, son and daughter etc. and the sex differentiation of male and female are the characteristics of the material world while this nomenclature has no meaning in the spiritual world. So it is not necessary for the God to be son of somebody. He is unborn and shall remain so till eternity.
Actually we have drawn the inferences of the body structure and the relationships from the lives of Lord Ram & Lord Krishna but they were the incarnations of the God Head and not the God themselves.
Both, Lord Ram & Lord Krishna had taken birth in this material world as a human being so they had to pass through the miseries attached to birth, old age, disease and death which are inherent in the material world.
But the real God Head lives in the spiritual world, which is free from all the miseries of the material world. And there he enjoys the life of ‘SAT’, ‘CHIT’ and ‘ANAND’ along with countless other Souls who merge with him after being liberated from the material world.