It is stated in the Bhagavad-gita (2.13):

"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. The self-realized soul is not bewildered by such a change." Such verses from the Bhagavad-gita or any other Vedic literature give valuable instructions on the occasion of someone's passing away. By discussing such instructions from the Bhagavad-gita or Srimad-Bhagavatam, a sober man can certainly understand that the soul never dies but rather passes from one body to another. This is called transmigration of the soul. A soul comes into this material world and creates bodily relationships with a father, a mother, sisters, brothers, a wife and children, but all these relationships pertain to the body, not the soul. Therefore, as described in the Bhagavad-gita, dhiras tatra na muhyati: one who is sober is not disturbed by such phenomenal changes within this material world. Such instructions are called tattva-katha, or real truth.