So this jñāna, even this jñāna, that change of body is not there. Throughout the whole world, big, big professor, big, big educationist, they do not believe in the next birth—99.9%, they do not. But this is a fact. There is. Tathā dehāntara-prāptiḥ. Kṛṣṇa says. And we understand this also. Kṛṣṇa gives this example: dehino 'smin yathā dehe kaumāraṁ yauvanaṁ jarā (BG 2.13). This child is becoming kumāra; a kumāra is becoming boy; boy is becoming young man; young man is becoming old man. So these changes are going on; still, he does not know that "After this old body is finished, I shall have to accept another body." So this is ignorance. Therefore we have to take knowledge from the most perfect Personality of Godhead, Kṛṣṇa. This is real knowledge.
So jñānaṁ te ahaṁ sa-vijñānam. Sa-vijñānam means with practical application. As there is theoretical knowledge and practical knowledge in scientific advancement, so simply theoretical knowledge will not help me. Theoretically I may know that I am not this body, but practically it must be known. If not, if I am not this body, then I am soul. Then I am working here in this world only for my body. What I am doing about my soul? That is knowledge. Suppose I have got this coat and pant and hat. If he simply tries . . . dry clean the coat and do not put any food in the stomach, how long this civilization will go on? Starving. So the whole world is in disturbed condition because there is no spiritual food, only material cleansing the shirt and coat. That is going on. Like cats and dogs, they are interested with the body.