The spirit of Bhagavad-gītā is mentioned in Bhagavad-gītā 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-gītā should be taken or accepted as it is directed by the speaker Himself. The speaker of Bhagavad-gītā is Lord Śrī Kṛṣṇa.