Tathā dehāntara-prāptiḥ (BG 2.13). As the body is changing, there are so many children, they will also become old like me. But the spirit soul is there. In the presence of mother, although the body is changing, the mother knows that "My son is there." Although from babyhood the son has grown to boyhood, the body, original body, child's body, baby's body, is not existing, the mother knows that "My boy is there."
So this is commonsense understanding. People do not understand it, very nice common sense, that the body is changing but the soul is there. Exactly the same example: the mother knows that "My boy, my child, although he has changed body, now he has grown-up, say, fifty years old, but my child he is. He is my child." Where is the difficulty to understand? Anyone can understand. But people do not believe in the transmigration of the soul.