The spirit of Bhagavad-gita is mentioned in Bhagavad-gita itself. It is just like this: If we want to take a particular medicine, then we have to follow the directions written on the label.
We cannot take the medicine according to our own whim or the direction of a friend. It must be taken according to the directions on the label or the directions given by a physician. Similarly, Bhagavad-gita should be accepted as it is directed by the speaker, Lord Sri Krishna, Himself.
If we want to derive benefit out of the Bhagavad-gita, then we have to follow some rules and regulations, otherwise, how can we understand? It is not an ordinary book of knowledge that you purchase from the market, and read it and consult dictionary, and you understand. Otherwise, Krishna would not have told to Arjuna, “The Bhagavad-gita is now lost. I am therefore speaking to you.” Why? “Because you are My devotee.” So one has to become a devotee like Arjuna and must be ready to understand the Bhagavad-gita as Arjuna understood. Then the spirit of Bhagavad-gita can be understood. Those who are envious of Krishna as the Supreme Personality of Godhead have no bona fide access to the great literature.
The non-devotee’s approach to the teachings of the Gita is something like that of a bee licking on a bottle of honey. One cannot have a taste of honey unless one opens the bottle. Similarly, the mysticism of the Bhagavad-gita can be understood only by devotees, and no one else can taste it. One who has a little faith in Bhagavad-gita should learn from a devotee, because no one else can perfectly understand it’s purpose. When one searches for a devotee and fortunately gets a devotee’s association one actually begins to study and understand Bhagavad-gita.