Thousands of people went off to work that day, just as they'd done day in and day out, just as we all do, only this time they didn't return. The same thing could happen to any of us, any day, any time. Death from an accident, or sickness will come upon us, for some sooner rather than later. We are constantly reminded of our mortality as we see examples of such deaths in the news, only the reminder given on 11 September was shockingly magnified. Remember your own mortality, don't fear it.
Death is simply the final act of a single incarnation.
Through it we return to the spiritual realm. Our souls will then continue on their journey of growth, to include other births, lives and deaths. To find out more about this process, read some of the books listed on our reference page. Don't fear death, accept it. Many religions teach you to fear death, fear hell, fear God.