Prabhupāda: So first of all, Kṛṣṇa explained that "We are not this body." The first instruction was given:
- dehino 'smin yathā dehe
- kaumāraṁ yauvanaṁ jarā
- tathā dehāntara-prāptir
- dhīras tatra na muhyati
- (BG 2.13)
The first instruction of spiritual life is to understand that, "I am not this body." The example is given, very simple thing, that I am present, although I remember that I had a small body lying down on the lap of my mother. I remember, when I was six months old, I was lying down on the lap of my elder sister, and she was knitting. I still remember that. So everyone, we remember that we had a small body, and then another small body, then another small body. Those bodies are gone. I have got a different body now, but I remember that I had all these bodies. Therefore the conclusion should be for the sober man that "Although we have changed so many bodies, I, the person, the soul, am existing." Therefore Bhagavad-gītā says, tathā dehāntara-prāptiḥ (BG 2.13). Similarly, when I shall give up this body, I shall accept another body. This is the beginning of understanding that, "I am not this body. I am living in this body just like I am not this coat, but I am living within the coat."
There is very vivid example in the Bhagavad-gītā. If we read, we can understand that "I am not this body; I am spirit soul." When this realization is there that, "I am spirit soul," ahaṁ brahmāsmi . . . the exact word used in the Vedic literature, ahaṁ brahmāsmi. That stage has to be attained in human form of life. In the animal forms of life, this understanding that, "I am not this body, I am spirit soul," in the animal stage of life it is not possible to understand.