Bhagavad Gita is a non-religious book in the sense it is a spiritual treatise detailing vital issues of life following which any human being world over belonging to any religion, faith or belief can indulge in teachings of Bhagavad Gita to reach cosmic end of life, state of enlightenment.
Though spirituality is part of religion but also totally out of it! Religious practices (indulging in rituals) practically gained nothing in life. However indulging in spiritual precepts contained in Bhagavad Gita one can easily cut across shackles of karma to become a pure soul atman.
The ultimate goal of life for all human beings on mother earth was liberation from cycle of birth and death forever. This cannot be achieved indulging in religious practices. Following one sacred text the revered Bhagavad Gita one can easily reach God in one’s lifetime. Reaching god, gaining enlightenment meant the same. In Hinduism self realization, god realization also meant the same.
Despite being religious or non-religious, the ultimate goal of life for all human beings on mother earth always remains the same, reaching God at the earliest. Becoming a Mahavira, Gautama Buddha Jesus Christ or Prophet Mohammed is not a matter of choice but the requirement of soul atman, the spirit residing in our heart.
Born a human being we are lucky to indulge in Bhagavad Gita to reach cosmic end of life. Why postpone matters for next manifestation when we can indulge in spirituality in present life.
The teachings of Bhagavad Gita are universal in nature and not a proprietary of Hinduism alone. Even while following ones religion one can indulge in teachings of Bhagavad Gita.