I am eternal, the body is not eternal. This is the fact. Antavanta ime dehā nityasyoktāḥ śarīriṇaḥ (BG 2.18). Śarīriṇaḥ, the owner of the body, is eternal, but not the body. In so many ways Kṛṣṇa is explaining about the material condition of this body. But those who are not very intelligent, with poor fund of knowledge, it is very difficult for them to understand. Otherwise, things are very clear. This point is very clear. That at night I forget this body, and in daytime I forget the body at night. This is a fact. Similarly, I may forget the body of my last appearance, last duration of life, or I may not know the future body. But I will exist, and the body may change, but I'll have to accept another body, which is temporary. But I, as I exist, it means I have got a body. That is spiritual body.
So spiritual body is existing, and spiritual advancement means first of all to know spiritual identification of myself. Just like Sanātana Gosvāmī went to Śrī Caitanya Mahāprabhu after retiring from his ministership. So he first of all said that ke āmi, kene āmāya jāre tāpa-traya (CC Madhya 20.102): "Actually, I do not know what I am, and why I am subjected to the miserable condition of life." Therefore the miserable condition of life is this body. Because I get . . . in dream also. When I get another body, sometimes we find that on top of the very tall bamboo or tall mountain, I am just now, I'm falling down. And I'm afraid, I sometimes cry, "Now I am now falling down." So this body, this material body, which body I belong to, which I am . . . actually, I do not belong to any of these bodies. I have got a separate spiritual body.