The Vedic knowledge was thus imparted unto the heart of Brahmā, the first living being in the material creation. It was Brahmā who related this knowledge to the sage Nārada Muni. Similarly, the Bhagavad-gītā was spoken by the Personality of Godhead, Śrī Kṛṣṇa, to Vivasvān, the presiding deity of the sun, and when the aural chain of disciplic succession was broken, Lord Kṛṣṇa repeated the Bhagavad-gītā to Arjuna on the Battlefield of Kurukṣetra. At that time, Arjuna took the role of disciple and student in order to receive transcendental knowledge from Śrī Kṛṣṇa. In order to drive out all misgivings which the gross materialists of the world may have, Arjuna asked all relevant questions, and the answers were given by Kṛṣṇa so that any layman can understand them. Only those who are captivated by the glamour of the material world cannot accept the authority of Lord Śrī Kṛṣṇa. One has to become thoroughly clean in habit and heart before one can understand the details of the anti-material world. Bhakti-yoga is a detailed scientific transcendental activity that both the neophyte and the perfect yogī can practice.
The material world is only a shadow representation of the anti-material world, and intelligent men who are clean in heart and habit will be able to learn, in a nutshell, all the details of the anti-material world from the text of the Bhagavad-gītā, and these are in actuality more exhaustive than material details. The basic details are as follows:
The presiding Deity of the anti-material world is Śrī Kṛṣṇa, who exists in His original personality as well as in His many plenary expansions. This personality and His plenary expansions can be known only by anti-material activities commonly known as bhakti-yoga, or devotional service. The Personality of Godhead is the supreme truth, and He is the whole anti-material principle. The material principle as well as the anti-material principle is an emanation from His person. He is the root of the complete tree. When water is poured onto the root of a tree, the branches and leaves are nourished automatically. And in the same way, when Śrī Kṛṣṇa, the Personality of Godhead, is worshiped, all details of the material worlds are enlightened, and the heart of the devotee is nourished without his having to work in a materialistic way. This is the secret of the Bhagavad-gītā.