"jatasya hi dhruvo mrityur
dhruvam janma mrtasya cha
tasmad apariharye ’rthe
na tvam socitum arhasi" (Bhagwat Gita: Chapter Two verse 27)
"Sri Krishna said: One who has taken his birth is sure to die, and after death one is sure to take birth again. Therefore, in the unavoidable discharge of your duty, you should not lament."
This truth of life & death is essential & is a natural course of life. Below story also describes that truth:
"A rich man asked a Zen master to write something down that could encourage the prosperity of his family for years to come. It would be something that the family could cherish for generations. On a large piece of paper, the master wrote, "Father dies, son dies, grandson dies."
The rich man became angry when he saw the master's work. "I asked you to write something down that could bring happiness and prosperity to my family. Why do you give me something depressing like this?"
"If your son should die before you," the master answered, "this would bring unbearable grief to your family. If your grandson should die before your son, this also would bring great sorrow. If your family, generation after generation, disappears in the order I have described, it will be the natural course of life. This is true happiness and prosperity."