Śrī Kṛṣṇa, the Supreme Personality of Godhead and the ideal spiritual master, spoke the philosophy of Bhagavad-gītā to Marshal Arjuna, His disciple. Here is a perfect example of the relationship between the spiritual master and the disciple. Arjuna was a most intimate friend of Śrī Kṛṣṇa, and thus Śrī Kṛṣṇa explained to him the essence of all scriptures, in the philosophy of Bhagavad-gītā.
Because we are always very busy in the discharge of our worldly duties, generally we do not wish to understand any philosophy except our mundane philosophy of the stomach and allied subjects. We have extended many branches and sub-branches of this philosophy of the belly in various directions, and thus we have hardly any time to understand the philosophy of gaining eternal life—for which we are perpetually struggling life after life.