Śrīla Prabhupāda Says

     Therefore this Bhagavad-gītā yoga system, which is very old... Forty millions of years before, ago it was spoken. And before that it was also spoken. That is not stated here. Because it is eternal. Avyaya, purātanaḥ, old.

     So who is qualified to understand Bhagavad-gītā? You can understand. Those who are not bhaktas, they can also understand superficially. Just like one has got the bottle of honey. If one thinks that “I have got the bottle of honey. Let me lick up the bottle,” so licking the bottle, what taste you will get? The bottle has to be opened and see what is there. (laughter) And if a rascal thinks that “I am licking this bottle, I am eating honey, I am tasting honey,” he’s a rascal number one. Simply.

     So similarly, if one is not bhakta, if one is not Kṛṣṇa’s devotee, that rascal cannot understand Bhagavad-gītā. Plainly. Plainly it is stated here. First of all, try to become the devotee of Kṛṣṇa. Then try to understand what is Bhagavad-gītā. Not by your scholarship or by your speculation.

Then you’ll never understand Bhagavad-gītā. If you have to understand Bhagavad-gītā, then you have to understand by the process as stated in the Bhagavad-gītā, not by your own mental speculation. This is the process of understanding. Bhakto ’si me sakhā ceti.

[Bhagavad-gita: 4.1 Montreal, August 24, 1968]