Answer by Niraj Bidawatka
When one understands that he is not this body, but a spirit soul, and then further comes to understand that the spirit soul is the eternal servant of Krishna, he gets enlightenment. Such an enlightened soul transcends the cycle of birth and death and goes back home, back to Godhead.
The entire Bhagavad Gita was spoken by Krishna to enlighten us about this fact. The last instruction of Bhagavad Gita is mam ekam sharanam vraja: “Just surrender unto Me”. When one gets enlightened that one is a part and parcel of God, one immediately surrenders to the will of the Supreme Lord.
Such enlightenment is possible only through the aegis of a guru, or spiritual master. It is the guru, who enlightens the soul that he is not this body but a spirit soul, which in turn is a part and parcel of God, or Krishna.
Arjuna was enlightened because he accepted Krishna as his guru. In the beginning of the Bhagavad Gita, you will find that Arjuna was babbling like a mad man throughout the first chapter but Krishna did not give him any instructions. It was only when Arjuna surrendered and accepted Krishna as his guru, did Krishna impart the secretive and most sublime knowledge.
So one gets enlightenment only when one approaches a guru. Therefore the Bhagavad Gita states tad viddhi pranipatena (4.34): Approach a guru. The Bhagavatam also states the same thing – tasmad gurum prapadyeta: Surrender to the guru. The Vedas also state tad-vijnanartham sa gurum eva abhigacchet (Mundaka Upanisad 1.2.12): If you want to get enlightenment, then approach a guru.
But the problem is that we do not want to accept a guru and therefore we do not get enlightenment.