The first man was created in the likeness and image of God. God is spirit and can do anything, go anywhere etc. . . When Adam ate the fruit of the tree of knowledge, there was a change. Before the change, there was no death for man. After disobeying God, death entered into the world of man.
The flesh of man will die but the spirit will abide forever. God did not make the flesh that man has today. We are now in the flesh of disobedience which is rebellion against God.
There are two opposing forces. The flesh is against the spirit and the spirit against the flesh. The flesh is death while the spirit is life. Paul wrote it best when he asked, "Who can deliver me from this body of death?" Only God can deliver anyone.