Spirit is described... We have already discussed on this point that the spirit is eternal. Na hanyate hanyamāne śarīre: [Bg. 2.20] "Even after the destruction of this body, the consciousness is not destroyed." That continues. Rather, consciousness transferred to another type of body makes me again alive to the material conception of life. And that is also described in the Bhagavad-gītā. Yaṁ yaṁ vāpi smaran bhāvaṁ tyajaty ante kalevaram [Bg. 8.6]. At the time of death, if our consciousness is pure, then it is sure that next life is not material. Next life's pure spiritual life. But if our consciousness is not pure at the point of the verge of death, just leaving this body, then we have to take again this material body. That is the process going on by nature's law. We have got our finer body. This is gross body. The body which you are seeing, which I am seeing, this is gross body.
Just like shirt and coat. Within your coat, there is shirt, and within your shirt, there is a body. Similarly, the pure soul is covered by shirt and coat. The shirt is mind, intelligence and false ego. Mind, intelligence and false ego. False ego means that the wrong conception that "I am matter. I am something, product of this material world." This wrong conception makes me localized. Just like because I have taken my birth in America, therefore I think myself American. Because I have taken my birth in India, therefore I think myself as Indian. But as pure soul, I am neither Indian nor American. I am pure soul. Because this is designation. This American, or Indian, or German, or Englishman, or cats and dogs and this and that, black and white, all these are designations. Spiritual consciousness means to become free from all these designations.
Prabhupada's lecture - Śrīmad-Bhāgavatam 1.2.17 San Francisco, March 25, 1967