This Kṛṣṇa consciousness movement, we are worshiping the Supreme Personality of Godhead, the supreme leader. Human society cannot work without leader. Anywhere you go, any country, any nation, any society, any community, any family, there is a leader. So the Vedas instruct that there is a supreme leader. Nityo nityānāṁ cetanaś cetanānām eko bahūnāṁ vidadhāti kāmān (Kaṭha Upaniṣad 2.2.13). This very important mantra in Kaṭha Upaniṣad.
You have heard the names of Upaniṣad. They are Vedic literatures. Originally, the Veda was one, Sāma Veda. Then it was divided into four: Sāma Veda, Atharva Veda, Ṛg Veda, Yajur Veda. Then the Vedas verses were explained in Upaniṣads. There are 108 Upaniṣads. Then the whole conclusion was made shortened, cream. That is called Vedānta-sūtra. And again, this Vedic knowledge was, I mean to say, compiled in simple way for understanding of less intelligent class of men.
That is called Mahābhārata. And in the Mahābhārata there is one chapter which is called Bhagavad-gītā. Bhagavad-gītā is only a chapter of the great history of India, Mahābhārata. And then Vedānta-sūtra is described in Śrīmad-Bhāgavatam. So Vedic literature is very old. Nobody can trace out the history. So far we understand, it is not man-made. It is coming out from transcendental world by disciplic succession.