2.13: As the embodied soul continually passes, in this body, from boyhood to youth, and then to old age; similarly, the soul also passes into another body at death. The self-realized soul is not bewildered by such a change.
SINCE EVERY LIVING entity is an individual soul, each is changing his body at every moment, manifesting sometimes as a child, sometimes as a youth, and sometimes as an old man-although the same spirit soul is there and does not undergo any change. This individual soul finally changes the body itself, in transmigrating from one to another; and since it is sure to have another body in the next birth-either material or spiritual-there was no cause for lamentation by Arjuna on account of death, either over Bhisma or over Drona, for whom he was so concerned. Rather, he should rejoice at their changing bodies from old to new ones, thereby rejuvenating their energy. Such changes of body are meant for varieties of enjoyment or suffering by the living entiy, according to one's own work in this Iife. So Bhisma and Drona, being noble souls, were surely going to have either spiritual bodies in the next life, or at least life in godly bodies for superior enjoyment of material existence. In either case, there was no cause for lamentation.
Any man who has perfect knowledge of the constitution of the individual soul, the Supersoul, and Nature-both material and spiritual-is called a Dheera, or a most sober man. Such a man is never deluded by the change of bodies by the living entities.