I want to know, why human die? What is the meaning of life? I could die tomorrow. What's the meaning of all these things?
Not only humans die. Other animals die too.
From the perspective of evolution dying of old animals gives way to a new generation, better adapted to a changing environment.
I do not recognize a higher meaning of life. Nature exists billions of years without animals. Nevertheless from the perspective of the single human individuum: We are able to choose a meaning for our own life. And if we are fortunate, then we succeed in doing so.
For most human beings, meaning itself is enough reason for existing. One could fundamentally replace meaning with pleasure as a basic unit of meaning, which better fits with other life forms too.