Great question. I belive it is because the devil makes us suffer. In Revelations 2:10 Jesus says, "I tell you, the devil will put some of you in prison to test you...Be faithful, even to the point of death, and I will give you the crown of life." What Jesus is saying is that when bad things happen to us it is the devil who is causing harm, only to test us. The devil does prevail in taking people's lives. Personally one of the strongest Christians I've ever known died out of the blue. The autopsy showed no reason of why he died. I believe that it was the devil taking away one of God's strongest followers.