Why are people really afraid of death?

Luther:

Because with dying you have three images: death, sin and hell. The more you muse about those three, the more ominous they become. Death takes his power from the weakness of our nature, sin from the weakness of our conscience and hell from the weakness of our faith. These images want to take us into their possession, and where that happens the person is lost and he forgets God totally.

What do you have to do with those frightening images?

Luther:

You do not have to see them as they are themselves or in those who are lost, but in the saints and in Christ. Some are overcome by death, remain in their sins and are damned. But you have to close your eyes to that. Look on the saints and on Christ, who died in God’s grace. You have to engrave that image into your mind. Christ showed us Himself at the cross against the three images with which the devil disputes us. He is the image against death, because He is risen. He is the image against sin, because He has taken them on Himself and He has overcome them through His obedience. He is the image against hell, because He was abandoned by God as one condemned, but yet He was the beloved Son.