When God created the world he did not intend that we would die. Instead, his desire was that we would live with him forever. Why then do we all die? The answer is that God gave us free will. Unfortunately, tempted by Satan, we used the free will that God gave us and disobeyed him, thereby choosing death over life.
God did not make death,
nor does he rejoice in the destruction of the living.
For he fashioned all things that they might have being;
and the creatures of the world are wholesome,
and there is not a destructive drug among them
nor any domain of the netherworld on earth,
for justice is undying.
For God formed man to be imperishable;
the image of his own nature he made him.
But by the envy of the devil, death entered the world,
and they who belong to his company experience it.
Thankfully, Jesus came to redeem our sins and pay the debt of our sinfulness. Because of his love for us, even though we suffer physical death we can be raised though him and live in his presence forever.