An atman is the life sap as per Bhagavad Gita. It is the Prana, cosmic energy that manifest human form. The journey of life belonged to this atman, spirit within human beings. This atman is also the master and controller of human life on mother earth.
Lord Krishna in Bhagavad Gita is allegorically atman existing in human beings. The teachings of Bhagavad Gita are available to entire mankind all the time but we failed to hear dictates of Bhagavad Gita coming from within our heart.
Ego within human beings (Aham in Hinduism) stopped one from listening to voice of Lord Krishna from within. At any given point of time only one can dictate, eagerly ego or atman from within. Travelers of spiritual path who succeed demolishing their ego in totality can distinctly hear dictates of Lord Krishna coming from within our heart. Almost entire Bhagavad Gita is within our reach.
I have done it all my life from six years of age. My ego from six years of age was zero by default, maybe resulted from karma of previous lives. I was also 100% truthful from beginning of life. So much so that voice of Lord Krishna from within haunted me all the time. At that young age I did not know what it was all about and how to handle it.
It took me more than two years to understand it. Thereafter it was never looking back. I have been guided by Lord Krishna in Bhagavad Gita from the very beginning of life. By grace of God Almighty my spiritual journey has truly been a blessing for me all throughout.