We hate death because we love life. How can one leaves his beloved parents, wife and kids, lovely car, cosy home, cool friends, memorable moments and vacations... Except if he know's what is waiting for him after his death... Believing in life after death makes one aware of what's waiting for him, and works for it as long as he's living... That includes doing good for oueselves then for people without counting it. Living without loving life to drawning... Commitment and moving forward.

death is not horrible horrible are the pains of life

我觉得吧，因为死亡对于我们是未知数，我们无可预料它的到来。 I think maybe it's because death is unknown to us and we cannot foresee its coming.

because it means leaving, we can't see people we love.

It's to do with the fear of the unknown.