Prabhupada's lecture - Śrīmad-Bhāgavatam 1.15.21 - Los Angeles, December 1, 1973
So similarly, this body is dead. That's a fact. It is dead from the very beginning. Because it is matter. Matter is always dead. So this body made of matter, bhūmir āpo 'nalo vāyuḥ [Bg. 7.4]—earth, water, fire, air. This external body is dead, but it is living on account of that small spark of spirit. That is the real meant. That we understand from Bhagavad..., dehino 'smin yathā dehe [Bg. 2.13]. Dehinaḥ, the small spark, spiritual spark, he is within this body. This is the first understanding of spiritual knowledge. You must know. This is the beginning of Bhagavad-gītā. When Bhagavad-gītā was taught to Arjuna, Arjuna was lamenting for this body. So Kṛṣṇa, when He was accepted Arjuna's spiritual master, śiṣyas te 'haṁ śādhi māṁ prapannam [Bg. 2.7], then He advised him that "You are talking like a very learned scholar." Aśocyān anvaśocas tvaṁ prajñā-vādāṁś ca bhāṣase [Bg. 2.11]. "You are talking just like you know..." Just like our so-called scientists, they speak as if they know everything, but real thing they do not know. That is zero. What is spirit, they do not know.
They are thinking this body. And according to Vedic knowledge, if one is misguided on the bodily identification of ourself, he is animal. He is animal. He may be Ph.D., D.H.C. or something, but he is animal. Sa eva go-kharaḥ [SB 10.84.13]. Because he does not know how the body is moving. And neither they can discover anything. When the body is dead... It is dead from the very beginning, but it was moving. Just like so long petrol is there, the motorcar moves. But as soon as there is... Now there is crisis. So how their motorcars will move? They are concerned. So why their crisis? Because the petrol is the life of the movement of the motorcar. Similarly, that spiritual spark, or spirit soul, is the petrol of this body.