As the embodied soul continuously passes, in this body, from boyhood to youth to old age, the soul similarly passes into another body at death. A sober person is not bewildered by such a change." (Bhadgavad-Gita, Chapter 2,Text 13)
Srila Prabhupada explains: In the modern age, people are so uneducated that they cannot understand the body is changing at every moment and that the ultimate change is called death. In this life one may be a king, and in the next life one may be a dog, according to karma. The spirit soul is in deep slumber caused by the force of material nature. He is put into one type of condition and again changed into another type. Without self-realization and knowledge, conditional life continues, and one falsely claims himself a king, a cat, or a dog. These are simply transformations brought about by the supreme arrangements.