If we engage ourself in the service of Vāsudeva, the Supreme Personality of Godhead... Vāsudeva is another name of Kṛṣṇa. Because Kṛṣṇa appeared as the son of Vasudeva, and Vāsudeva means all-pervading also... So Kṛṣṇa is both. He is the son of Vasudeva. He appears. He accepts. Ajo 'pi sann avyayātmā bhūtānām īśvaro 'pi san. Although He is the original source of everything, still, He appears like a human being, becoming the son of His devotee like Vasudeva or Nanda Mahārāja, like that, or Mahārāja Daśaratha. That is his option. He can appear from anywhere.
So Kṛṣṇa is perfect. If we take lessons from Kṛṣṇa, instruction from Kṛṣṇa, then we get perfect knowledge. That is the process of studying Bhagavad-gītā. If you accept Kṛṣṇa as ordinary human being, then we are befooled. Avajānanti māṁ mūḍhā mānuṣīṁ tanum āśritam (BG 9.11). We should accept Kṛṣṇa. Why should we accept? Because all the śāstras accept. Kṛṣṇas tu bhagavān svayam (SB 1.3.28). Īśvaraḥ paramaḥ kṛṣṇaḥ sac-cid-ānanda-vigrahaḥ (Bs. 5.1). Sādhu-śāstra-guru—that is the evidence. According to our Vedic knowledge, we shall accept a thing when it is proved by Vedic evidence. Therefore Veda means knowledge, perfect knowledge.
So sādhu-śāstra. Śāstra means Vedas, and sādhu, saintly persons, and guru. Saintly person means who abides by the śāstra, Vedic knowledge. One who does not accept Vedic knowledge, so, followers of Vedas, they do not accept him as an authority.
Even Lord Buddha, He, because he did not accept the authority of Vedas, therefore in India he was rejected. Although Lord Buddha appeared in India, for some time many people became followers of Buddhist religion, but later on it disappeared from India. It went outside. What was the reason? Because Lord Buddha did not accept the authority of the Vedas. So although Lord Buddha is accepted as incarnation of God... We Vaiṣṇava, we worship Lord Buddha, keśava dhṛta-buddha-śarīra jaya jagadīśa hare. Nindasi yajña-vidher ahaha śruti-jātam.
Śruti-jātam. The statement in the Vedas, that is called śruti-jātam. Nindasi. Because his mission was to establish animal, to stop animal killing. Sadaya-hṛdaya darśita-paśu-ghātam. Therefore he had to reject the Vedic principles because in the Vedic principle, in the sacrifice, there is recommendation sometimes, not always, about sacrifice of the animal. But his aim was, mission was, to stop animal killing. Therefore for the time being he rejected the Vedic authority, because people will take advantage that "In the Vedas there is recommendation for sacrificing animals." So just to stop, to take this advantage, he said that "I do not accept the authority of Vedas." Therefore he was accepted as atheist. Veda nā māniyā bauddha haya ta' nāstika. That's a big story.
Anyway, we have to accept knowledge from the perfect person. This is the sum and substance. Unless we take knowledge form the perfect person, our knowledge is defective. Therefore Arjuna is asking, "What is this prakṛti, material nature? What is puruṣa?" Puruṣa means who is trying to exploit (break) ...he is also prakṛti. Prakṛti. Just try to understand, woman, strī. But if one strī wants to enjoy another strī. So how it is possible? That is not possible. There must be puruṣa. So puruṣa, these living entities, although they have dressed like puruṣa, they are not puruṣa. They are prakṛti. Jīva-bhūtāṁ mahā-bāho (BG 7.5). They are superior prakṛti, but not puruṣa. But they are trying to be puruṣa. This is called illusion. If a woman dresses like a man and wants to act like man, that is artificial. That is not possible. Similarly, a living entity is not puruṣa; he is prakṛti. But because he wanted to enjoy this material world, nature has given him a dress like a puruṣa, and he is falsely trying to enjoy another prakṛti.