Why Do We Fear Death?

Most people want to live forever. Why?

If it is simply because we enjoy our life now, or could imagine enjoying it if all our trials were gone, then consider this: perhaps we would get bored of living even the best life? It seems unlikely that it would happen in 100 years, or even in 1000 years, but perhaps, after 10,000 years we would be bored. Maybe we would actually want to die.

If we are suffering illness, poverty, or misfortune, we think we shall be satisfied on the day it ceases. But there too, we know it is false; so soon as one has got used to not suffering one wants something else.
— Simone Weil, Three Essays on the Love of God

Or do we fear death because we fear judgement?

Say “If the last home with God is to be for you alone and no one else, then you should long for death, if your claim is true.” But they will never long for death, because of what they have stored up with their own hands: God is fully aware of the evildoers. [Prophet], you are sure to find them clinging to life more eagerly than any other people, even the polytheists. Any of them would wish to be given a life of a thousand years, though even such a long life would not save them from the torment: God sees everything they do.
— Qu’ran 2:94–96, Trans. by M.A.S. Abdel Haleem

Or do we fear death because we are not intended to die?

For the creation was subjected to futility, not willingly, but because of him who subjected it, in hope that the creation itself will be set free from its bondage to corruption and obtain the freedom of the glory of the children of God. For we know that the whole creation has been groaning together in the pains of childbirth until now. And not only the creation, but we ourselves, who have the first fruits of the Spirit, groan inwardly as we wait eagerly for adoption as sons, the redemption of our bodies.
— Romans 8:20–23, English Standard Version

Does the fear of death keep us trudging along?

To sleep; perchance to dream. Ay, there’s the rub,
For in that sleep of death what dreams may come,
When we have shuffled off this mortal coil,
Must give us pause—there’s the respect
That makes calamity of so long life.
— Hamlet III.1

Is it reasonable to fear death?

Let us reflect in this way, too, that there is good hope that death is a blessing, for it is one of two things: either the dead are nothing and have no perception of anything, or it is, as we are told, a change and a relocating for the soul from here to another place. If it is complete lack of perception, like a dreamless sleep, then death would be a great advantage… for all eternity would then seem to be no more than a single night. If, on the other hand, death is a change from here to another place, and what we are told is true and all who have died are there, what greater blessing could there be?
— Apology 40d–e