If we accept that "I am this body," then we are no better than the cats and dogs, because their concept of life is like that.
When we understand that "I am not this body...," As Kṛṣṇa wanted to impress upon Arjuna in the beginning of His teaching of Bhagavad-gītā: "First of all try to understand what you are. Why you are lamenting in the bodily concept of life? You have to fight. Certainly you have to fight with your brothers and brother-in-laws and nephews, other side. And you are lamenting. But first of all understand whether you are body or not." That is the beginning of Bhagavad-gītā. He tried to make him understood that you are not body. So these instructions were not for Arjuna. For everyone. We have to first of all learn that "I am not this body. I am spirit soul." Ahaṁ brahmāsmi. That is Vedic instruction. And as soon as you come to this point, if you are firmly convinced that you are not this body, that is called brahma-bhūta (SB 4.30.20) stage, Brahman realization stage. That is knowledge, real knowledge. Knowledge, advancement of knowledge for eating, sleeping, mating, that is animal knowledge. The animals also, the dog also knows how to eat, how to sleep, how to mate and how to defend. So if our education is only on these points... The dog is eating according to his nature, but we are also eating in a nice plate, nicely cooked food in a nice table, but the principle is eating. That is not advancement, that "I am eating in a better plate in a better place than the dog; therefore I am advanced." But you are eating, that's all. Similarly sleeping. You may sleep in a very nice apartment, six story building or 102nd story building; a dog is lying on the street. But when he sleeps and when you sleep, there is no difference. You cannot know whether you are sleeping in a skyscraper building or on the ground, because you are dreaming something else which has taken you from your bed. You have forgotten that "My body is lying there on the bed, and now I am flying in the air," dreaming. So this sleeping method, if you improve, that is not advancement of civilization. Similarly mating. The dog has no social custom. Whenever there is another she-dog, he mates on the street, and you may do very silent in a secret place, but the mating is there. But people are learning how to mate like dog. So in this way defending. A dog has also his defending measures. He has got teeth and nails. He can defend himself. And you might have atom bombs. But the measure is defending. That's all.
Therefore śāstra says that human life is not meant only for these four principles of life, bodily demands. There is another thing. That another thing is brahma-jijñāsā. Athāto brahma jijñāsā. A human being should be inquisitive to learn what is Absolute Truth.