Why do all men have to die?

All men have to die because death entered through the fall of man and sin. The body, referred to as the old Adam, is dead because of sin and under the curse. This mortality is part of Adam's transgression, and every person will die unless the Lord comes to translate them.

Les explains that in Romans 8:10, Paul writes that if Christ is in you, the body is dead because of sin. Les identifies this body as the old Adam, noting that Adam and the flesh were all under the curse. Death came in as part of the fall of man, and so all men have to die. However, Les points out that this body will die unless the Lord comes to translate us, referring to the hope of glory—Christ in you. This mystery, revealed in Paul's epistles, was not made known in the Gospels or Old Testament, but is now proclaimed among the Gentiles.

Romans 8:10

And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness.

Why does every person have to die if the body is under the curse?

Because the body is the old Adam, and the flesh came under the curse through sin. Death entered as part of the fall of man, so all men have to die. Every person dies unless the Lord returns to translate them.