Purpose of life as per Bhagavad Gita does not directly pertain to manifest human life. Lord Krishna in Bhagavad Gita says ultimate goal of life always remained liberation from cycle of birth and death. Human beings keep endlessly rotating in cycle of birth and death until our soul atman, the spirit within reaches state of absolute purity.
After death of present body the released soul atman, our real self within would again manifest a new body to start new journey of life. This cyclic rotation of life continues until human beings indulging in spirituality detailed in Bhagavad Gita succeed reaching stage of self realization, god realization termed enlightenment in English.
No doubt human beings are powered with an independent will, power of discrimination exercising which one separated truth from false, right from wrong. Still, human beings were only a pawn in the cosmic journey of life, the actual master and controller being our soul atman existing in heart.
If human beings so desire not to indulge in spirituality to reach cosmic end of life, it is okay with god. For this very reason God Almighty ordained a long journey of 1.1 million manifestations in human form before human beings succeed reaching state of absolute purity as a soul atman.
Indulging in spirituality to reach cosmic end of life is noble indeed. We can do it in present life by following teachings of Lord Krishna in Bhagavad Gita or keep it pending for future manifestations. But one thing we must always remember, the present manifest physical form is limited to present life only. Based on residual balance of karma at the time of death the released soul atman would manifest a new body in next manifestation.
When very young between eight and nine years of age I finally decided to end the cycle of birth and death forever. And hence started my indulgence in spirituality detailed in Bhagavad Gita.
Cosmic purpose of life is different from goal of life for the manifest physical human form. As a human being we could reach any bracket of life only to repeat the same journey again and again. I did not want to do that. Understanding my cosmic goal of life once and for all, I plunged wholeheartedly into abyss of spirituality, path of unknown uncharted territory. I was prepared to take all risks and that too unconditionally as everything spiritual always was unconditional.
If we did not succeed in our spiritual pursuit of life, we just could not question god!
Most human beings, seekers I have come across had a conditional approach to spiritual life. They were wrong in their surmise. Everything relating to God and spirituality was always unconditional. Whether or not we reach our goal, all success on path of pure spirituality is totally dependent on our efforts, God Almighty Brahman had absolutely no role in it.
Prime reason why terminology like total surrender to god is used in field of spirituality! Unless a total surrender is there, unless we agree to demolish our ego in totality, we could never succeed on spiritual platform. Only by demolishing ego we stepped into higher domains of consciousness.
Understanding Bhagavad Gita and the cosmic purpose of life becomes easier if we had 100% faith in God. Absolute faith in God simplifies our spiritual journey. Before embarking on spiritual journey we must be 100% clear about our ultimate goal of life, to what extent we wanted to pursue spirituality in its present shape.
Bhagavad Gita says if we feel we cannot clear the entire journey in present life time, we must indulge in spirituality at least partially to attain whatever best level possible in prevailing circumstances. Just feigning ignorance in matters spiritual is nothing better than animal life.