Our source of knowledge is Kṛṣṇa or Kṛṣṇa's disciples. That is our . . . evaṁ paramparā-prāptam imaṁ rājarṣayo viduḥ (BG 4.2). This is the source of knowledge, avaroha-panthā, knowledge coming from higher authorities. Just like Ṛṣabhadeva is giving knowledge to His sons. That is natural. Sons take advice from the father. That is the beginning of knowledge. If a little child asks the father, "My dear father, what is this machine?" the father says: "My dear child, this is called microphone," so when the child says, after hearing from the father, that "It is microphone," that is perfect knowledge. The child may be a innocent child. He does not know. He is not a scientist. But when, after hearing from the authority, father, if he says: "It is microphone," that statement is correct. There is no mistake. Similarly, we may be fools and rascals. That's all right. But when we receive knowledge from Kṛṣṇa, who says, asmin dehe, dehino 'smin, yat kaumāra yauvana, tathā dehāntara-prāptiḥ . . . (BG 2.13).
When Kṛṣṇa says that within this body there is the living soul, and the living soul is transmigrating . . . tathā dehāntara-prāptiḥ. As we are getting different bodies in this life also, from childhood to boyhood, from boyhood to old body, then what is after old body? Tathā dehāntara-prāptiḥ: you get another body. But we do not know what kind of body we are getting. Where is that science? Where is that education that there is dehāntara-prāptiḥ, there is transmigration of the soul, and there are so many different types of body? Suppose in this body I am very comfortably situated, I am a very big man, or very great minister, politician, everything is all right—but in the next life, if I am going to get the body of a dog, who can check it? Nature's law will go on. At that time, as minister or big man, if you dictate that "Give me a body like this," oh, that will not be heard. You will get a type of body according to your karma. Karmaṇā daiva-netreṇa jantor deha upapatti (SB 3.31.1). According to your karma, you will get a type of body. This is nature's law.
Prakṛteḥ kriyamāṇāni guṇaiḥ karmani sarvaśaḥ (BG 3.27). We are completely under the grip of nature's law. We cannot change it. If we challenge that, "There is no death," no, death will come. That is nature's law. And if you want to stop death, then that is another process. That is described here, tapo divyaṁ putrakā yena sattvaṁ śuddhyet (SB 5.5.1): You have to accept this process of austerity by which you will purify your existence. Then you will get deathless life, eternal. Yat gatvā na nivartante tad dhāma paramaṁ mama. Tyakvā dehaṁ punar janma naiti mām eti kaunteya. This is the science. This Bhāgavata literature, this Vedic literature, is giving you information how you can revive your original, eternal life. Nityaḥ śāśvato 'yaṁ na hanyate hanyamāne śarīre (BG 2.20). That is the business of human life, not to become mad like hogs and dogs and simply work very hard—"Where is stool?"—and eat it and get some strength, and then enjoy senses. This is not life. This is not civilization.